Over Collecting of Debt

My debt with Creditworx was paid up in February 2014. I have send them e-mails since April 2015 to stop the debit order and to repay the instalments they have over collected back to me. You are getting provided with email addresses but when you send an email it gets ignored. In Jan 2016 they have deducted another instalment. When is this going to stop and when am I going to get my money refunded? PLEASE HELP!!!!!