Steam nonsense

CaviXxnX​ Your EA Account can only be linked to one Steam Account in its lifetime, (which means that your preferred Steam Account cannot be linked to your EA Account).

EA Help | How to link to an EA Account

As mentioned here by @EA_Pythia, you may be able to contact EA Support and ask if they can make an exception, (but there is no guarantee that EA Support would be able to).

EA_Pythia wrote:
EA has a rule that only one platform account of a kind can be linked to an EA account in its lifetime, even if you unlink the accounts.

You might be able to contact Support (try a different browser or device if you're having issues) and explain your situation there. They might be able to make an exception and link the accounts for you, but there's no guarantee for that.

I personally wish that we could link a different account, (however we cannot as the system is meant to protect our accounts in the event that we get hacked. (Although, the solution to that problem would be to make the player wait a bit of time to give the account owner time to recover their account in the event that they were not the one that had requested to change the linked accounts)).