If talking to their internal collection department is not working, consider filing a complaint with the BBB. It *might* motivate the bank to start a dialog with you.
Be careful how much detail you are putting in the BBB complaint. Some (most?) of their complaints become public.
*and*
Have you gone over your forbearance letter to see what the terms were? Did it say you had 6 months to get your finances in order and start paying? Did it say you need to reapply every 3 months? There "charge off" might be a mistake or something that was overlooked in the details.
I would think - and I could be wrong - that doing an electronic payment or mailing a check in - would start the process of paying them back. They would probably accept the check. In the past, I have had experiences with places that refused to take payment (like the hospital) so I had my bank send them a check every two weeks. Danged if they didn't cash every single one of those checks! Still were b**tholes, still wouldn't talk to me, still sent me to collections. And each time it went to collections, I produced the history of the every two week payments to the CA and the CA always returned the account right back to the hospital.
I am sorry that you are experiencing such a brick wall with communicating with the bank. I hope you can find a way around, over, or under the brick wall and get them to cash your checks/payment. And don't let them bully you into an agreement you can not afford. If possible, do payments every payday.
