As someone currently dealing with the same issue due to EA's asinine policy of any linked account only being able to link one in it's lifetime. If they suggest Merging the account just note it will not work since they keep the merged accounts information in the cloud in case you want to remake the account so even if you unlink Steam from the account it's still tied to said account. Worst linking policy I've have ever seen as well as sketchy data holding practices. Your best option would be to "VERY clearly have a advisor "IF" you can somehow get through to one Delete the account and specify that you want the account wiped "COMPLETELY" as they will say they have deleted the account when in fact they will have just made it dormant and stored it in their servers. Good Luck!!!
- Sincerely Annoyed Consumer