Retrieve an account I last used in 2017

Hello,

I had a kind of "big" account back in 2017 which I'd love to play again with.

It was linked to my Google Play Games account and to my Facebook account
We can see that I have a lot of achievements (10/13) on Google Play games, meaning I was indeed playing the game (through GPG):

Problem: I stopped playing at some point, switched to a new device AND also deleted my Facebook account

Now when I log in from a new device, my account is nowhere to be seen. My friends still have my account in their friendlist, meaning it isn't deleted.

Support gave me some troubleshootings links that weren't useful at all and said the account isn't linked to GPG or Facebook anymore. So far the support communication is very slow and doesn't help at all.

What can I do?