Wowcher complaint: Unable to get a response

I purchased two afternoon tea vouchers (4 people) for Cafe Concerto but due to Covid restrictions I was unable to use them because the outlets weren’t open. I contacted Wowcher using Messenger 15 days before the expiry date (19th May) and received a speedy reply saying the expiry date was extended to 31st August. Great so far until I tried booking and saw my voucher expiry date was still 19th May. Since then I have persistently contacted Wowcher explaining the problem and quoting reference numbers, email addresses, phone numbers etc but other than the generic reply promising to be in touch Nothing! The only reply I received a couple of weeks ago was to tell me the booking system has changed and giving a phone number. I phoned the number, made a booking for June 7th at Westfield, Stratford but they just told me to bring the vouchers with me on the day. The vouchers now say EXPIRED and it would be embarrassing to arrive with my family and be expected to pay full price. My reference number is 35823317. Wowcher are still offering afternoon tea at Cafe Concerto