6 or 12 months

I purchased glasses at Specsavers late November and had the remaining balance after medical aid payment put onto my Edgars account - and specified to the cashier for it to be on the 12 month plan. I now get a statement from Edgars and the amount is under the 6 month plan!!! when I called to the 0860 number on the statement they say I no longer have a 12 month option but every time I go shopping (whether its Edgars stores or CNA) the cashiers always ask 6 or 12 month plan. The person at 0860 says that the amount was put through onto my 6 month plan because the 12 month plan under one account has been s****ped but then why do I keep getting asked 6 or 12 months??? This was never communicated. I know I didn't use the 12 option recently because I reserve it for larger purchases.