Minecraft account only works demo what to do?

I had a Minecraft account some time ago, but I took a long break and got a new PC. I wanted to try Minecraft on this one. I was also able to log in and the account was there, but only the demo version was shown to me. I can't play the game normally even though I bought it. How do I get it that I can play normally again?

Did you buy Minecraft back then?