Ring Adjustment done Incorrect

I bought a ring on the 24th November 2014, only to find that the ring was small and had to be sent for re-sizing. I was asked to pay R150 and was charged on my Foschini account. The ring was sent and on my return to collect, the ring was now too big. The shop assistant told me that i need to pay another R150 for it to be re-sized again. I left the ring at sterns as i will not pay another money for their wrong measurements. I have already paid for the ring. This is bad service.