Billed for a course I cancelled a month after reg

I unfortunately dread having to come to UNISA because I just have no joy with how the staff handle the enquiries brought forward. I received an sms on the 13th of April 2015 stating I settle my account before facing a debt collector. I went into UNISA on the 23rd of April and went to Finance and spoke to a lady who printed me a statement with an outstanding fee of R514, I then told her that I cancelled the module on My UNISA a month later which was around March 2014 as I couldn't afford to carry on with the studies at that stage. She then said she will not be able to assist me and referred me to registrations department. I went there at the Humanities counter and was assisted by a gentleman whom I asked to check for an audit trail from my My UNISA account with the cancellation I did on the site, he couldn't find anything and referred me to Erna who said to me that she can't find anything which in turn says that I didn't send any cancellation. I asked for the cancellation process to see if what I read is what I'm being told. I didn't get one showed to me. I just don't appreciate how my enquiry was handled because I cancelled the module on the site 3times and no one can see it. How??