Unauthorised debit orders dates

I have insurance policies with Frank.net. Frank.net has had a bad tendency of debiting my bank account on the date I did not authorise when I took insurance policies with them. On the month of December they usually inform me with an SMS notification that the premiums will be debited before the date normal debit order date. This month(January) my bank account was debited before the debit order date without my knowledge and consent. I have sent numerous messages and get confirmation that I will be contacted shortly. I took the initiative to contact hellopeter to speed up the process. I would like to change from debit order to stop order because lately there's been unauthorised debit orders on my bank account.