Never use WONGA!!!

I am so disgusted with WONGA Finance SA, I took out a loan in 2018 and paid it back in March 2019 the full amount plus extra for the interest charged. A debt collector keeps calling me telling me I still owe and I keep sending through my proof of payment to Wonga and the debt collectors they so nicely handed me over to but nothing happens, every week it's the same thing! I will never use their service again because now it's affecting my record and their service is just shameful.