Unreliable ticket sales

Booked 2 x tickets for Afrikaans is Groot on 31/07/2018. I was allocated two seats and had to do the payment which I did. A week ago I received an email informing me that the seller is unable to provide the tickets I originally purchased. Don't worry. You can choose alternative tickets. Whoopie doo!!! Tickets were sold out months ago. I had to pay in order to secure the seats allocated to me. How come a week before the show I now do not have booked seats. Surely if I have paid for the seats allocated to me there cannot be a double booking. Obviously not. I smell a rat. Now I have an upset wife and I hope and pray my money will be refunded.