The chicken curry in economy was ok. The rest of the experience was and continues to be a true nightmare. I was scheduled to take flight DL73 from Amsterdam to Atlanta, having purchased a Delta Premium Select seat - to try for a change, as I had most recently flown the same route in Delta One. However, KLM and agents dressed in Delta uniforms put me in wrong lines to check in and check my luggage, the KLM agent badge said “trainee” and they had me waiting 35 minutes before a more experienced agent came over and finally said “oh of course he is all clear, including the covid test document” and information that I also provided physically and on both the Delta app and the KLM app. The more senior KLM agent apologized and said that my bags would make flight DL73 and I would also make the flight so long as I ran to the gate. I did just this, and despite multiple other passengers being escorted in front of me through security and customs, I ran very fast and was at gate E22 in Schiphol at 11:15, well before the departure time of 11:40 (plane actually departed at 11:44), and certainly over 15 minutes prior to departure/door close - being there 25 minutes before departure. Nonetheless, the gate agent literally saw me and said “Mr. (my name), we just closed the gate.” I was shocked but the same agent said that I would have “no problem” getting on board DL75 at 1pm, including in a Delta Premium Select seat, for which I had paid along with being a Platinum frequent flyer. She told me to wipe the sweat off myself, take a deep breath and that “transfers” at Schiphol would handle and confirm this new flight and details for me. I then stood in a mile long line at gate T6, where KLM and Delta transfers were supposedly being processed. At the same time, I called Delta twice, each for about 35-45 minutes, and Delta said they could not help me, and to speak with KLM. This was also a rude surprise as Delta and KLM used to work together much more smoothly. It was also a lie as I later found out that the Delta Globalist team can help in this situation. An hour later, I made it through the transfers line only to be told that KLM could do nothing other than sell me an entirely new ticket! I then called Delta again, and finally a woman named Alexa (Alexis perhaps) - I think - finally listened to and reviewed my information. She deeply apologized and said that KLM simply listed me as a “no show” which is infuriating and inaccurate. She apologized again and asked to speak jointly with someone at KLM (at Schiphol) because apparently no one at Schiphol actually works with or understands Delta even though these flights were operated by Delta and many individuals wore Delta uniforms. I have flown that route many times as well with no issues whatsoever, but this was a true disgrace for Delta and KLM. The Delta globalist team / Alexa asked to speak to the KLM gate agent. Thus as it was then 12:30pm, I had to run to gate E24 to continue trying to get on board the 1pm flight and put the Delta team in touch with a KLM agent. Finally, at gate E24, the same gate agent from the earlier flight (DL73/gate E22) said, “Mr. (my name), I think your bags are waiting by the plane but I don’t think I can get you or them on this flight either.” I was shocked again, but Alexa and I spoke via speaker phone on my cell phone with the gate agent and a team of 4-5 others that appeared to be with KLM or Delta at the gate based on their uniforms. They finally somehow managed to get me on board, but refused to seat me in the open Delta One seat or the four open Delta Premium Select seats, instead placing me in economy, oddly which the Delta website and app still do not show, instead showing that both flights DL73 and DL75 are still in my itinerary. I am utterly disappointed, shocked and amazed at the level of poor treatment, not to mention why would Delta - and the FAA not have this information clarified in their systems? My luggage still shows as being at Schiphol airport, and my seat was far worse than the mediocre Premium Select seat for which I paid, as the flight attendant spilled cola on me and laughed with other passengers around me about Delta platinum and Diamond status for some reason, apparently unaware that I am a platinum flyer. My Delta app and the website continue to show both flights (from yesterday) in my itinerary as if I am somehow going to fly one of those flights now(?), which is even more confusing. It also clearly shows that despite being Delta Premium Select, a seat for me was “not assigned,” which makes no sense. This was by far the worst experience I have had with Delta and my opinion of Delta went from almost 5 stars to about 1.5 stars due to these unfortunate and awful events.