Cell C is unprofessional and show no good faith

I cancelled my contract with Cell C in 2018. In 2020 i receive an email stating that i owe them. I therefore request a statement. I received nothing but a debit order of a R1.100. For what i dont. Who authorized the debit and who agreed to the value i have no idea. Their service is so terrible and i would never recommend them to anyone. Their customer service consultants are stipid and useless