I had a similar situation with bank a few years ago, not identity theft but rather some checks stolen out of the mail and cashed by the third party, and didn't realize it for a few months (so it was being the easy ach reversal point). I tried to escalate within the bank, must have talked with tier 2 support a dozen times.

What worked was to file CFPB (consumer financial protection bureau) complaints against both banks involved. At that point I got to talk to executive support, who is responsible for handling such complaints, and was able to get the two banks to talk to each other. Should've done that about 6 months or so sooner.