Dishonest business practice

We bought a device from them in September 2022. When we purchased the item, we asked the salesperson to supply us with the correct coils for the device. We then purchased the coils and the device from them. After attempting to replace the coils we noticed that these are incorrect coils that were sold to us. We went back to the shop to exchange them for the correct coils. This is when we were informed that they don't have stock of these coils. They took our details but after 4 months there was no response. We went back to them to find a solution. They weren't helpful and told us that this is our problem. We requested a refund but were told that this was not possible. This leaves us in position where we paid for a device which we can't use. This is very dishonest, and we believe that this is not the way of doing business.