poor service

I was called by Netstar at the beginning of last month and was told that the tracking device needs to be upgraded. I indicated that I want to cancel my contract. They agreed and said I would receive an email confirmation. To date, one month later no cancellation. I have tried calling numerous times, no answer. I used the automated WhatsApp and received no return call. I even emailed customer service, and no response. I am still being charged for a contract with a device that does not work. How do you explain that? Very disappointed in their poor communication and lack of customer satisfaction.