As stated , a communication like that is normally when you join a new provider , basically your old provider has to advise you of the impact /consequences of leaving , like if you were inside a minimum term and early termination charges apply , getting this type of communication when you haven’t signed up with a new provider indicates a mistake has been made , usually by someone who has used your address instead of the address they intended , the automated system generates the ‘sorry you are leaving ‘ communication…..
This communication should have a number to call if it’s a mistake (or even if it were a genuine attempt to change provider but the customer has changed their mind about joining that new company)
BT and EE and basically the same company so if the number you called was answered by EE and not BT isn’t really important, it’s if you said you had received this letter and it’s a mistake so you want nothing to change , and the person you spoke to said OK I can cancel this so you are not affected , did they say that ?
The rest of your post is not clear , do you have broadband or just a telephone ?
