Go to Builders - and get done by them

I went to Builders to get things done and instead got *****ed. I had to return an item and upon presenting the original invoice to the returns department they said the item had been returned already. Even though I still had the item and there was no stamp of the return on the invoice. I queried this and a manager came forward, looked at it and then went away. The manager then came back with what appeared to be a fabricated proof that it had been returned which I found very odd as it wasn't marked as refunded and I still had the product in my vehicle. I didn't have a lot of time so let it go for the time being however later went through my bank statements to check if it had been credited and of course it hadn't. This is very odd that a business like BH can purport that items have been returned when they haven't. They even went so far as to take the product back anyway despite saying same had been refunded. Can some one investigate this and let me know where the refund actually went? Perhaps there is some internal mismanagement/*******ion reminiscent of the Zuma years( the country is trying to rid itself of this kind of practice) I will take this to the highest level until I get a satisfactory explanation.