When I tried to play minecraft I was forced to make a new account and can't login to my old one

So I wanted to play minecraft and I tried to login to my account like I always did and instead of logging me into my account it forced me to make a new one.

Now every time I try to login, it puts me into this new one so how do I get my old account back?

before the time this happened I bought a laptop and registered or logged into a microsoft account so maybe that has done something? I don't know.

:)