I hope this doesn't turn into another *insert China Vendor* bash thread.
But....
As a rule of thumb, I generally don't order any lights over the $50 zone from any foreign vendor. For this reason alone. It is too much headache to return defective products. I am not sure that 100% of the fault falls in Banggoods lap. Granted, you would think they would have some sort of QC for expensive items shipped abroad. But, I can imagine that would be expensive depending on the volume of sales. It would be much easier to resolve if they could have some sort of Return label shipped with products and have a pre agreed upon shipping fee for returns. Like $10 or so. That way, when order a item, you know if you are not satisfied, it would only cost you $10 to return it. Something like that would be fair.
After you send all your Videos of the problem to BG, file PP claim and good luck.