Incorrect billing and service

For the past three months I haven’t been using the service but I keep getting debited each month. According to the terms and conditions this 4G sim is a pay as you use but I am being billed for something I didn’t and don’t use. I sent their customer service messageS of which they have not responded to as yet. They tried to debit this month as well and I haven’t used the sim. All I want is my money back since it’s not a contract. The reception has been atrocious hence the reason I haven’t been using the sim.