False information and miss leading sales gimmicks

I opened an RCS Builders account a while ago on the advice of the in store reps for a big purchase I needed to make. The recommendation in store from the RCS reps in both Builders Express N1 City and Makro Montague Gardens was that I could make my purchases over 60 months.I got my statement and it’s been out through at 24 months. When calling the RCS call center they state there is no 60 month option on their cards yet I have two receipts stating 60 month budget period. The 60 months was offered by the instore rep and the sales clerks. The I store reps even calculated the repayment amount for me over the 60 month period. Please advice urgently as I have incurred big additional costs I was wrongly advised off.