CANCELLED CONTRACT, HOWEVER STILL BEING BILLED

Signed up for a mobile data contract with TELKOM just before lockdown 20th March 2020, only to be shocked by the almost impossible usage, since both adults were at work and only an 8 year old who could possibly be responsible for 20G of data usage in under a week. I even had to to a top-up within 7 days - I cancelled the contract on the self-service option within the 7days, i received a cancellation number. I even quoted some of the Consumer Protection Act; the cancellation of the contrat was done within 7 day period. About a week ago i received an invoice for the month of May. Puzzled, as i had cancelled the contract. The sim card was not in use. I had taken out a data contract with another service provider. Since the 27th March, my attempts to contact the Customer service has been unsuccessful. Using COVID-19 as an excuse for pathetic customer service! Please help :-(