Need my gas heater

I bought gas heater 16/6/21. It was on special and i received additional 15% discount because i purchased online and it was my first order. I didn't receive it because they didn't have stock and they told me i have to wait till feb for stock. I have write to builders numerous time about my order and phoned their call centre with no success. Order no. ***. And they still have my money in their account.