So i'm new to United and had a bewildering experience today and I'm wondering if either a) I was spoiled by another airline 2) I was just flat out WRONG? 3) my incident was just a "one off". I'd truly appreciate any advice and I'll try to be succinct:

I bought a paid ticket in combo of first and Polaris biz from IAH-DCA-EWR-BOM in early 2019. (don't ask why the double connection btw, it worked for me LOL.) The original ticket was all in P class except for DCA-EWR was in Y b/c it was a single cabin aircraft on United Express. So there was a schedule change which I saw today and the new flights that I wanted were IAH-IAD-EWR-BOM. The IAD-EWR is now on a 737 so there is f/c avail so I knew enough to CONFIRM that I'd be seated in f/c all the way thru, before the new ticket was issued. I was told by the original phone agent that I'd be in coach for IAD-EWR b/c I was originally ticketed in coach for that portion. I explained why that was - was a single cabin aircraft and f/c not avail. He spoke to a supervisor then came back and said the supervisor said no, coach for that portion. I then spoke to a supervisor (not sure if it was the same one he spoke to) but explained to her and she said NO to f/c on that one flight. If I wanted f/c for IAD-EWR it would be an add/collect of about $117 I think. So by this time I'm getting pretty upset b/c the logic didn't make sense. Eventually, I hung up in frustration, called back, got another supervisor and the situation was resolved in about 3 mins, and no add'l add collect needed. First and Polaris business all the way through.

So I'm wondering w/ then w/ my initial questions: a)have I been spoiled heretofore by another airline or is this kind of inflexibility/illogic expected of United? b) am I just flat out wrong to request/ask for f/c for that one portion since it was now available and not expect to pay more or 3) did I just get a bad supervisor the first time?

I'd really appreciate ANY constructive feedback as I attempt to learn United's culture. thanks everyone and safe travels...