Worst service in history

**** poor service, cancelled my contract over 8 years back unit started drying my cars battery so arranged with them to get their unit removed. The first person I spoke to at Netstar requested that I make a bank transfer into their account and send the proof of payment and that is what I did. End of May 2019 Netstar on their own tried twice to debit my account without me giving them permission and for something that I already paid for. I tied speaking and getting hold of somebody at there accounts department to assist and I emailed them my bank transfer I made in February but yet end of April Netstar again tried debitting my account. Again tried making contact and send through my bank transfer that I did. Now today Netstar debitted my account. I feel I want to see a lawyer to help me settle this. Who gave them permission to debit my account without my permission.