Game poor product knowledge and customer service

So I bought a Russell hobs microwave at Game promanade Mitchell's Plain last year June... I used it for 2months then when I moved its been in the box since then when I took it out of the box it had some rust inside of it... My problem is the microwave is practically brand new and was stored in its original packaging and still got damaged and now they say the guarantee doesn't cover rust but I paid for a new product and it's still under guaranty which tells me they are quick to sell you something but doesn't disclose these important facts when selling you products, now the only leg they have to stand on is my word against the sales person who sold me the product... I told the manager I don't even want my money back I would accept a voucher so that I can buy me something else. The thing that upset me the most is if I had known all the specifics I would have made an informed decision not to purchase such a unworthy product