Bad service

I have cancelled my contract with this company in January 2025. They phoned me and said they'll send me a cancellation form and have to pay for January and February and send them a proof of payment. Indeed I did that. Kealeboga Montshiwa (Credit Controller) is the one who circulated the cancellation form I sent for their attention. The cancellation form was sent to all consultants and to me. To my surprise, every day after then, they phone, sending sms and emails that my account is in areas, that my payment has not been received and that payment is required urgently. I always keep on telling them that I have cancelled the contract with them. Different people phone, send sms's and emails, everytime I tell them and respond to them that I've canceled the contract but keep on sending sms's and emails everyday. The car that was installed with the tracking device was sold in January. I ended not responding to any of their emails as I'm tired of repeating one and the same thing.