Adidas ripping customer off

I ordered online and mistakenly chose the wrong size same-day I logged a query requesting the change in size and I was advised to wait for the order to arrive then change at the nearest store. Which I contacted Woodmead Adidas spoke to Ofentse and she had made the request the size 2weeks later I went personally to the store for the change and the size hadn't arrived and I was advised they'll keep following up..To date calls and emails by manager hasn't been responded to. Adidas online is staying that my exchange/return period has expired nothing can be done.. Please how can I resolve this as R2000 is alot of money to forfeit.