Why would I get a cheque when I never closed this account
This is a customer to customer self help forum, not a link to BT.
Call customer services 0800 800150 and ask them.
@Ralph4wrote:Why would I get a cheque when I never closed this account
Few reasons, you could be on a monthly payment plan and your account is in credit, this triggers a billing payment pause and generates a refund.
It could be you were given goodwill, this was then refunded to you and BT have no bank details, so a cheque is issued.
Ring 0800 800 150 and speak to the billing team, they'll confirm exactly why.