Still waiting for my gas heater.

I bought a Goldair Gas Heater on Monday 9th May 2022 and it gave me problems so I returned it on Tuesday 12th July 2022. When I arrived there the salesperson said that there are no more Gas heaters available so I said they just order from another Builder's Warehouse. They promised to call me back jntil today. When I do call, they say their lines are down. I still want to make my exchange because when I check online they have 26 Gas heaters in stocks so meaning they **** to me. I am still waiting for a response but Builder's Warehouse has the worst customer service ever. I would like this issue to be resolved ASAP because I am now without a gas heater.