HOME LOAD INCREASED AFTER 2 YEARS

I have had a home loan with standard bank since 2009, in 2016 we took a advance and a further advance in order to upgrade our home. 2018 i app**** for a substitution of debtors due to a divorce only to be told that the repayment in 2016 was calculated incorrectly and that my bond repayment amount will increase by approximately R1400. Because of my divorce there is already financial constraints, now standard bank due to what ever there reasoning is has further constrained my financial well being. Why am i being held responsible for a mistake made by standard bank staff ?