Ridiculous Billing,Charges and Harassment

Every month with out fail I receive a barrage of SMS from MBC. I have called and requested they stop sending me the SMS notifications. My account is set an a Debit order so never miss a payment. It is a good month if I don't receive less than 10 SMS from them. I called them on 04/01/2018 requesting them again to stop sending the SMS notifications. By 10am on the 05/01/2018 another SMS notification. 10 SMS received in November, 12 received in December. I called as least 3 times on 05/01/2018 to rectify this, got given 2 numbers to call and neither worked. Then was cut off when been transferred to the supervisor. I checked my statement and noticed that just from their collection fee, SMS charges and one of the Interests, more than half my instalment is been used up. Yes one of the Interests, I am been charged 2 different interest each month. At this rate I will never pay this account off.