I have upgraded my BT mobile plan to a EE plan but my BT plan does not seem to have been cancelled...and I am still getting charged for it.
this is a public forum please delete your account number for your security
During the order process, were you issued a PAC code ? this is used to port your old BT mobile number to your new EE mobile, this retains the same mobile number and also stops the BT mobile service and associated charges.
Has your number transferred to the EE SIM? If so the PAC transfer was successful & you have a billing error. As said earlier, a PAC transfer automatically cancels the original SIM.
If the number hasn't transferred after giving EE the PAC, then you need to ask them why.
PACs are single use & expire 30 days after creation.