Does the plan file a Form 5500-EZ? If yes, then it is even more important to preserve the plan's EIN. EFAST2 will be looking for continuity and likely at some point will send out a penalty letter if it doesn't get a filing that shows a final filing and assets going to zero for that EIN.
You may want to try to contact a compliance officer at the bank (not at the branch, and who hopefully know a smidgen about retirement plans), and have a discussion about the bank making an unauthorized change to the plan's EIN. You may want to salt the conversation by saying "IRS" and "compliance" a few times. You actually may be doing them a favor.
If this does not go well, then definitely follow Lou and David's advice!