Returned kit 3 month ago but you’re still going to charge me £50
If you call BT 0330.1234.150 with your Proof of Sending or your Proof of Receipt they can update your account.
This is just a customer to customer help forum, everyone here, including myself, are just customers and will not be able to deal with any issues relating to your account.
Try calling 0330 1234 150
You can message BT using the "message us" links on the help pages. That is usually effective.
https://www.bt.com/help/contact-bt