Unhappy with Customer Service

I bought an item from them, when it arrived it was over sized, i sent it back, they sent me a voucher to use with my purchase, the voucher did not work, i informed them over 2 months ago that the voucher was faulty it has been an up and down for the past 2 months to either get my money back, credit to my Zando account or another voucher that works, all i get is an email from another customer service agent or Facebook message which is of no help. Their telephone also not working. I am a loyal client of Zando and now i must experience this Customer Service, i am honestly not happy. All i really want is for someone to get back to me with "proper" feedback so i can shop again.