Be careful of Protea Bookshop and the exchange rules

Bought grade 12 study guides at protea bookshop in Carlton Centre on the 14 January 2019, the slip is written no refunds only exchange. The timeframe for exchange is not stipulated on slip. I called the bookshop to ask about the exchange, the line was not getting through. On the 6th day after purchase I visited the store, I was told they do not exchange study guides, while there is no notice that says that, you only know when they tell you. Secondly they say they exchange within 5days of purchase, my 5days was falling into the weekend (Sunday), I was suppose to return them on Sunday, while their website shows that they don’t open on Sunday. I asked about since when do they operate on Sunday, they said since last month, they just didn’t update the website as yet. How was I suppose to know that while their line is also not going through? the response with regards to the line was, we just moved in so phones are not working properly. I asked to see the Manager, they said He/She is on leave and no one is acting on behalf. I didn’t get any assistance on the way forward.