Bad customer service and incorrect billing

I've had my wifi router contract with Telkom since 2019 and for the past few months I've noticed that my debit order amount changes on a monthly basis. The statements are inconsistent and they are billing me more than what I have contracted with them. I have been calling their customer care line however I don't get through to anyone to assist me with my account issue. This is the second time Telkom does this to me and till date I have not received a refund. I cannot even cancel my contract with them because they don't answer any calls and their automated service just repeats the options.