Builders refund

I bought a power station online, while waiting I saw status showing complete. Then I called and emailed them, to my shock they advised that the stock is finished and they will refund me

I have been calling to follow up on the refund with no success. This is the worst experience ever. All I want is my refund as they failed to deliver the item. I've been called multiple times by their agent promising refund in 72 hours but from Beginning Jan till now I'm still waiting... Worst service ever