Parkdean Resorts complaint: Caravan rental refund

My parents book a holiday last year but because of covid it was cancelled. Do the got a voucher and re booked a bit closer to home. In January my father sadly passed away.
My mother asked me to phone and cancel for her, at the time we had great customer service. We were told she would get her refund within 28 day. So after a month, there was nothing. I phoned back to ask if there was a problem only to be told the person on the first call shouldn’t of got a refund. But a manager would phone. Which never happened. I’ve phone back 4 or 5 time waiting for over a hour. The last time I even got to speak to someone, I explained everything only for the line to go dead. I phone back straight away to be told I was 17th in line. I really could wait another hour. Now it seems like my mum has lost over £600. That at this moment is very much needed