Safari Outdoor Waders

I purchased a set of waders ( March) that leaked on the first time i used them. I returned them to Safari Outdoor who sent them to their supplier who replaced them. the second set of waders leaked on the first use. I returned them to SO a month ago. SO supplier passed a credit and i was told that i can have a voucher to the value of the waders to spend in their shop. I visited them to tell them that i want a refund as there is nothing I want to buy in their shop. this was two weeks ago. Bank account details were sent on the same day as the visit. Follow up e mail was sent last Thursday. No response, I called today and then received an e mail , "we can only give shop credit, there is nothing wrong with the product but could be that it is not been used as intended " . They are accusing me of lying and for not used as intended, please enlighten me what they are intended for.