Just Pay Now refusing to help with their system problems take my money for something I don't have...

I went to purchase two heaters from Builders Warehouse Emalahleni. The system said an error occurred and I tried again an did it again but on the app it's said their's a problem so I went and pay cash. Went on the app and Justpaynow stil took the money from my account. Spoke to Builders and on their side the transaction did not go through only the one I paid cash for. Now Justpaynow are refusing to give me a refund and Said it's Builders problem but it doesn't make sense because I don't have an account with builders?? Now who is going to stop this??? Justpaynow are very unprofessional And unhelpful...