Received a T4 for money I was never paid

As the title says, received a T4 for somewhere I haven’t worked in over 5 years. I called them and they told me there was a cheque for a retroactive pay, which was issued in 2025 but they never sent the cheque out. It was a nice surprise. They told me they would deposit the cheque. They never did.

I called them, they said they’d send the cheque. They did but it was dated April 2025. Bank refused to deposit it, I called them, they said to do it through a phone app - so I did and it bounced.

They are no longer answering my messages or phone calls. I had already prepared my taxes for the year but didn’t submit them and now unsure what to do.

Who do I contact about this at the CRA?

I am filing my taxes as a Québec resident but just moved to Ontario.

Thanks