Refuses cash refunds but you have limited options!

My husband bought my son a pair of Adidas sandals in Somerset, that were too small. I went to the branch in N1 City to exchange it for a pair of Nike Sunray protect sandals. They did not have a 10 and I was told that this particular sandal only goes up to size 9.5.I bought it but it was too small so I took it back to the store and was told they do not do cash refunds. I called their head office and was told that's the policy and that's final and I should've read their policy that was up at the till(not N1, or Somerset has it up \at the till") I asked about a voucher and was told that its valid for 3 months. I went to get the voucher and again"