Very similar situation happened to me. I called, they tried to tell me it was an equipment change, but it wasn't, then they tried to tell me it was because somebody needed the seats, implied someone with a disability, but the seats they moved me from do NOT have extra room. I just wanted to be closer to the front. Long story short they couldn't help me or give me a decent reason why it happened.
Only change was departing 5 minutes later, but arriving about 40 minutes later.
I did get an email though.