Bad service

Where do I start ,took out a loan from wonga finance they start to debit my account and decide they decide to skip one month and the continue debit the following months .About three months ago I start getting 5 to 8 calls every single day , then the person wants me to confirm my I'd number and personal details before they can say were they calling from ,I refused to give any detail and decided hangup and call the number back which came out to wonga. The consultant informed me that I'm one month in arrears and do I want to make arrangements, I asked for which month and they could not provide any details . I decided to draw a bank statements which showed there was one month they did not debit me .But they still act like I missed a payment and the fault was on there side, they actually wanted to charge me interest on the amount they missed .The problem with all of this there is no person at wonga you can complain to they just dont care about there customers. They care more about the security of there company ,what company do you know asked for your I'd before you know who you speaking to.