I had a similar experience a few years ago with my mother. I was talking to her on the phone about my DS changing school and mentioned the time my DSis and I were to change school - about 30 years ago, and she completely denied it.
DSis and I were sent to a private girls school which I always hated, never fitted in, and in 1st and 2nd year I was bullied by a group of former friends. Our parents told us that they'd decided to send us to the local state school, and that we'd be moving school in a few weeks time. I was delighted - just so happy! Then, 2 days before we were supposed to change school, we were told that it wasn't happening. My parents said that they'd gone into the new school for a meeting to discuss some details of us starting there and the Head Teacher had told them what to do when we were bullied. My parents said that because the teacher said "when" not "if" we were bullied that they had changed their minds and we weren't to go there after all, but stay in our current school - where I was already being bullied! I was completely distraught - weeping, wailing, screaming. I shut myself in my bedroom, cut up all my school photos - I just wanted to destroy something, anything, I think.
That whole experience of being given hope, then having it snatched away from me was excruciating, and like the OP, affected me deeply.
And my mother said none of that had happened. I couldn't believe it. I went through all of those details with her. I told her I remembered overhearing a conversation between my parents and my granny about us leaving the private school and my granny offering to help with the fees and my father saying it wasn't about the money. According to my mother, none of that happened, and we were never going to that school.
After that conversation with my mother, I really started to doubt my own memory or thought I was going mad.
Fortunately, I have a sister! I phoned her, told her what had just been said, and my sister remembers it all just the same as I do, including how distressed and upset I had been.
I have no idea at all why mother does this. She denies other things as well. Anything that doesn't reflect well on her choices as a parent is dismissed, ridiculed or denied.
I don't get it.
for you OP. It's horrible to have your own painful reality negated by your own parents.