A Building Loan cannot be converted to an Access Bond

I have a bond with the Standard Bank that was an Access Bond. The bond was originally entered into to purchase an empty stand with the purpose of building a house. Standard Bank extended this bond in order that I can build a house. The bond was converted from an Access Bond to a Building Loan. The house is now complete and I wanted the bond to be converted to an Access Bond as it originally was. As it stands the balance on the bond shows "Available balance" R*** amount. On applying to have the bond converted to an Access Bond, I am told that it cannot be done as a Building Loan cannot be converted to an Access Bond.

Please tell me I am missing something? What about the "Balance available"?