They are robbing me

I bought a pair of earrings on the 18 of march 2016, they were R310 and I paid with R400 then the cashier said I should give her R10 so she can give me R100 change. When I got home I realised that the price that was on the earring does not correspond with the one one the till slip. The price on the slip was R210 and my change was supposed to be R190, I went back to the store the very same day. I explained my problem to the supervisor she then called the cashier and explain everything to her and she agreed that she gave me R100 not R200 but still they did not refund me but told me that they have to check first if their cashier was over or short before they can refund me and promised to call me on Wednesday the 23rd of March but the did not call until I decided to go today and check. So when I got there they told me that their cashier was not over so they can't refund me they have to call head office first and I should wait for their call again. Now I think they are not taking me seriously because they are busy sending me from Pilar to post. I feel like truworths is robbing me