Sounds like you have tried everything already, so it would be a hardware escalation: 1-800-821-2797 or 1-800-835-6100.
I installed bridge version 655911_WC6515 using Versalink Firmware Install utility fwdl188.8.131.52ww-20201006-1 on an Xerox WorkCentre 6515 DN MFP
After a successfull update i got the following error message: Cyan Toner (C) Cartridge Mismatch error notification
All my toners where above 80% before this update and they worked perfectly fine. I even printed out several pages before i performed this update.
After that i continued to update firmware version 656611_WC6515_E using the same Versalink Firmware Install utility but the problem still remain.
I have tried,
1. Rebooting it. Power off + remove power coord.
2. Remove catridge -> shut down / start -> shut down -> install catridge -> start
None of the trials worked.
The reason i updated the firmware was because the old version didnt seem to work with Mac OS Big Sur 11.0. What should i do?