I had a similar issue. It was a mess. I had 2 accounts. A Facebook log in and a game center log in with my Apple ID.
I was going around darting my event Dinos and switching at each one so both accounts got it. I thought it took too long to close my app and turn game center on/off so I decided to go into settings while logged into my game center account (my main) and I hit the link with Facebook thing.
Man, so what this did was override my main account on game center and made my alt account my game center account as well as Facebook log in. No matter what I did by logging out of Facebook and trying to log in with Game Center. Or turning Game Center on or off and trying. All roads ended with my alt being the only account I could log into! It was a mess. So for like a week I couldn’t log into my main account. I was freaking out.
I had to contact support and they had me create a new guest account. Provide my main account numbers support key as well as the support key for my guest account. They pulled my data from the main account and put it to the guest account. Then I was able to get my profile back for my main. They separated the 2 accounts.
Now my main account is through Facebook and my alt is through game center. It’s backwards from how it was originally but I could care less as long as I’m able to access both accounts.
Don’t fear that your account is forever lost and gone because it’s not. As long as you have your support key you are ok.
If you haven’t already tried, go into your phone settings and turn off your google play account fully. Then long in with Facebook. See if that fixes it. You can also go into Facebook on their website and go into the settings there to find your apps Facebook is linked to and completely delete and forget that it is linked to it. Maybe that will help.
Whatever you do, make sure you have your support key for your account always. Then ludia support can help you out.
I feel your frustrations and I hope they can help you out.