Unclear information from Netstar

I joined Netstar 9 years ago. Thankfully I never had to make use of their service. Recently I was offered a better premium from another security company and decided to make the switch. I contacted Netstar and gave notice. The same day Calvin Govender sent me an e-mail to confirm that they received the notice. He gave me a reference number and said a consultant will call me. A lady called me and asked me why I never made use of Netstar Go and I told her that I didn't need the service and that I anyway cancelled my subscription with Netstar. This month there was again money deducted from my bank account. Yesterday I sent an e-mail to Calvin Govender to ask why the money was deducted. I never received an answer back. When I called now a lady Rodene told me that this money is for the service they gave to me in August. On previous occasions I was told that you pay in advance like you do for your house rent. Now all of a sudden you pay in arrears. I asked them to send me the contract where that is stipulated but haven't received anything yet. I am not happy with this and I need Netstar to refund me for this premium. I will not encourage anyone to make use of their services in future.