Head office reluctant to solve my case. i have sent them proof of a settlement letter from my bank

Very very bad service. Unprofessional. I logged a complain with them. Its almost a month now and they responded once and promised to assist. Firstly they indicated that they cannot locate my account but monthly they are sending me emails advertising their stuff. It looks like they are reluctant to clear my name to the beurewo as my account was settled in February 2020. i supp**** them with all my details till to date including the proof letter from my bank.