drones direct- customer service is poor

We purchased a DJI Phantom 4 from drones direct and immediately started to have problems with it.  This information was emailed to DJI Technical who confirmed there had to be a fault with it.  Drones Direct reluctantly took this back to check for a fault.  They carried out there own tests and were confident that there was no fault.  We however were experiencing the fault every time we used it.  The tests were repeated over and over again and they kept insisting there was nothing wrong with it.  They said they would take it back from us and give us a partial refund while taking hundreds of pounds from us a re- stocking charge!!!! They eventually agreed to send it back to DJI to be tested who confirmed straight away it was faulty.  So we eventually got a refund book this took 3 months to sort out!!!!  If they had sent this back to DJI to start with as we asked them to or done their own tests correctly it could have been dealt with in a couple of weeks.- Oh and the fact that they wanted to charge us to restock it and have some other poor person given the faulty drone!!!!