Replacement aurpod doesnt work

hello,

I bought a replacement airpod because I lost one of the airpods and I disconnected the case and the airpod I still had. When I tried to connect the one using the old case it didn’t work, I tried resetting my airpods multiple times and tried it on different phones but every time I got the pop up message saying: Mismatched airpods

The airpods in the case do not belong to you and don’t work together.

Under this text it shows the left and right airpod saying they are not mine.

Although one is new the other one was mine for over a year and it did fine but it cant even connect now and it isnt mine anymore?

Can someone help me?

Thanks already