Return voucher not processed

I placed on order number*** and requested a return and reference number of *** was issued. However my voucher has not been processed on the system since Thursday last week. Now I cant use the voucher to buy what I want and Zando's last delivery date for this year is 23 Dec. I have tried calling in several times in the last two weeks and the phones rings unanswered for more than 10 minutes . I emailed three weeks back when I had a query and I only recieved a response only this Sunday. I am really frustrated because this is an online shop , emails are only attended to after three weeks and phones are never picked .Clearly I will not get my order as my voucher has not been processed and I cant buy anything as my voucher is hanging I dont know with who