ADT Fidelity accounts

I have been paying the B*****kspruit Trust ADT/Fidelity accounts monthly for the last 2 years. From October 2023 they started sending me statements saying the account is in arrears. In December 2023 the accounts dept sent a letter to say we need to pay in 7 days. I sent proof of payment of the monthly accounts to the email I received the letter from with no response. Now I get another statement showing we are still behind on our account so nothing has been done with the evidence submitted.