Harrasment, Poor Service and Robbing customers

I finished paying Fonechoice on 30 April 2020 which is the day that my laptop contract ended with them but still their consultants are still harassing me with calls demanding payment, I emailed them all my proof of payments and have requested a paid up letter which to date I am still waiting for it. Fonechoice keeps on debiting money from my bank account for the account that was settled in April. When I call their offices, I'm put on hold or being transferred from consultant to another and what they do after their harassment calls they send me numerous text messages that reads as follows: Mrs Mali, your query 617014 has been resolved to your satisfaction. Regards, Forechoice. I don't know what more must I do with these mafias. I want all my money they have debited on my account and my paid up letter then they can leave me in peace.