Me haidressers Will not honour gift vouchers bought in their own store tavistock, United Kingdom Internet

My partner bought me a hundred pounds worth of vouchers for me hairdressers in their own shop. I was so excited to use them, as it happened i fell ill and gave them to my sister as a gift. My sister booked a appointment and went to get her hair done, when she arrived she mentioned she was using vouchers for ME hairdressers. 

The hairdresser said she could no longer accept payment with a voucher because the owner of the hairdressers no longer paid her back. My sister was disappointed and called me up, i rang them and asked to speak to the manager but they said he was out and would get him to call. 

Finally after hours of waiting the mangers wife called, instead of appoligising for the error, she asked what colour my voucher was, and what shape it was. I explained this was irrelevant i just wanted my money back if they were not going to honour them. She then became quite snotty on the phone and told me if i sent my sister in they would cut her hair now, for me this was no good i wanted my money back. 

After about a hour of arguing they said they would drop the money back at the hairdressers and i could go and collect it. 
The cost of running my car there alone cost me 30 so i was well out of pocket, when i got there the receptionist was very lovely and told me it had happened to a few people, i will no longer ever use me hairdressers again.