Customer service very bad

I would like to know why I am being called everyday several times a day when my account is supposed to be paid up. I have been in arrears 2 months and got a message that I qualify for 50% discount if I must settle the account. I then called Wonga and spoke to a guy and explained about the 50% discount. He then said yes that’s correct and arranged a once-off debit order for the account to be settled. The debit order went off and all and now it’s been 2 months past already and I am still getting calls and spoke to numerous different people explaining my story then they say yes, they will sort it but never does!!! Now I am getting messages every time to say I have been handed over to Nimble Credit Solutions. I have whatsApped them but no response. I have emailed them but no response. What do I do with this situation? Can anyone please assist as I feel I want to sue them now. Why waste my time like this? And why waste your time as well on a settled account where you could have utilized the time to chase up a bad debt client? Please help me!!!