Island Hotel Horrid Service

We booked on the 29th March 2019 and paid in advance at the Island Hotel in Durban for a wedding to check in on the 9th August my sister in law also booked in January to check in on the 8th Aug and she got called on the 5th Aug to be told we don't have a booking anymore as they have a group booking. I never got a phone from them and wouldn't have known anything if she didn't tell me. When I called them they said they where going to call me and this was after 12pm they then said they want to put us in a place further from where we booked and away from the wedding house a place of their convenience and my sister in law said she called them 2 weeks ago to check if everything was still ok and they said it was all 100% fine and now a few days before we go down to Durban we have no accommodation and with it been a long weekend we to get accommodation took us half the day to sort this problem out and costed us double the amount now. They are rated as a 3 star hotel but their customer service is pathetic. The Manager name is Dion who hasn't even gotten back to us once to ask us if we came right with our accommodation I called today to check how long our refund is going to take as we gave him the banking details yesterday and he was off today and no one even responded to the email to say that all is in order and it has been done. They waited from January and March to tell us that we don't have accommodation because of this group booking which they took. How do you double book in the 1st place after taking our money from 2 people we know of so far.