Over Billing

I struggled with internet from mid may and called their customer services, wrote emails and I was promised that the matter will be escalated, I was patient and allowed them to fix my query , got a new sim but still it was not working. I requested to cancel in June and the consultant promised that they will fix my internet connection and that was unsuccessful. I then cancelled the sim card beginning of June but I was billed for the services I did not use only to be told that I am being billed for the previous month, mind you I did not use the internet since mid may but I had to pay for the service. The sim card was cancelled officially but they billed me again this month saying its for June. I am being ****** and I am not satisfied with their customer service or their ability to solve customer issues.