Takealo.com sent an opened iPhone and refusing to offer a full refund

I purchased vouchers last year which I added to my store credit. I requested different voucher dominations, and this was declined. I then asked for a refund which was also declined. I then proceeded with purchasing a brand-new iPhone but when it arrived today, the plastic was already removed, and the seals were broken.

I am furious that they sent be an open iPhone (not brand new as advertised). I do not want a store credit and they refuse to refund me. I should be entitled to a new phone as advertised or my full refund, but they still keep refusing!