Unauthorised deduction from Yellodata

I have had a contract with Yellodata for years and never had any problems with them until August this year. They deducted an unauthorised amount from my account on an unauthorised deduction date. I was informed that they will reimburse me for the amount deducted. Since August, I have only received a portion of the amount back and after numerous emails and calls to them, I have not received any indication when all of my money will be paid back to me in full via email or telephonically. I have have since cancelled my contract with them.