release of suretyship

In 2005 I app**** for a personal loan of R25000.00 and my mum signed surety for the loan. Nothing was explained to us about limited/unlimited suretyship. Any way the debt was settled in full in 2009. Absa did not release the suretyship. In 2012, I app**** for a consolidation, which was approved, now my mum wants to sort out her financial affairs and we have been advised that the suretyship still stands. I approached more than 3 branches to assist and none were able to, they just pushed me from pillar to post.Absa are now claiming that the suretyship can not be released as my mum signed unlimited surety. why was this not explained to us and why was the surety not released when the initial debt was settled. This is rather unfair, bottom line I need the surety to be released