Price fixing

I buy molicare nappies very month for my disable son 4/5 packets a month, by this time i know the price of the nappies off by heart. I usually buy it at Dis-chem The Glen price R275. for small. I went to Southgate and paid R304 went to Maponya and paid R304 per pack, online the nappies are R275 per pack why is it that these other stores charge different prices from The Glen and if the price went up how come it went up with a whole R29 after we had an interest rate cut?