Pay back my money

I wanted to renew my insurance with momentum so I went on their website to check how much it would cost. Since I was in a hurry I quickly browsed through and saw the price was 408 per month for the student medical aid. Once I got the money I paid R410 into their momentum account only to find out that momentum only accept 6months or 12 months upfront payments. Since I didn't have money for 6months upfront payment, I requested for a refund of my R410 via email. They send me a document to fill and send back. I have filled the document and sent it three times now and haven't got a single response from them. I just want my money since I am not covered by momentum.