There are no such things as EE engineers, apart from the mobile phone masts etc , EE can send out agents on their behalf (Openreach, Qube , or contractors working on behalf of Openreach effectively on behalf of EE ) but you state EE engineers.
Why are EE ( that’s if you are correct and the person had EE identification) visiting a BT customer, that makes no sense.
@natashajay Agreed. As long as the 14 day cooling off period hasn’t been breached, the plan should be simple enough to cancel, so one wonders what the issue is here with Customer Service?
@natashajay How long left on the cooling off period? If this goes on past the cooling off period, it’ll get worse as your Nan will be trapped in the contract.
As far as I'm aware being an account manager doesn't give the ability to speak on behalf of the account holder. It is a very limited role.
You have been given multiple pieces of good advice and next steps to take. May I politely suggest you pursue those avenues rather than simply posting on this forum where nobody is in a position to actually do anything other than offer advice.
The 14 day cooling off period starts from when the "service" went live. As long as you notify the seller, in this case BT within 14 days of that date that you wish to cancel they are required to cancel the contract.
Because in this instance, assuming it was within the 14 day period that BT were notified it makes no odds that they are now stone walling or ignoring that request as the "clock" has effectively been stopped from when BT were first notified.