Difficulty in finding out what I owe

In 2010 we moved to the UK for a couple of years to study and for work experience. We ended up spending 5-years abroad and upon returning I opened a Prestige bank account at Standard Bank. When I received the card Standard Bank placed a restriction on the card preventing me from using it as a debit card. They said that I had an outstanding credit card debt with the bank and they provided me with a number for credit control which I was instructed to contact. I tried calling the number on a number of occasions but the phone just went unanswered. After about the ten attempt I finally got through to them and they had absolutely no idea why I was asked to call them as they could find no records on me. I gave up at this point and eventually opened an account at Absa. <br> I have since app**** for a homeloan and was declined on the grounds that I have an outstanding credit card debt of over R24,000. I had absolutely no idea I had owed this amount and based upon my experience above I have no idea who I must approach to find out more details regarding this debt in order that I can discuss means to settle this and clear my credit history. Extremely frustrating!