As a point of interest Trading Std do not deal with the public. You have to go via citizen's advice. Who may forward it to them, but do not expect any action from them. As local councils have cut them down to next to nothing.I suggest write to dealer's MD and Kia's UK chief. Start by saying you have a fault which needs fixing, and if no action is taken will then be going to Trading Standards. Then clearly explain the problem. Finish by reiterating your need for a fix under warranty (Inc a courtesy car whilst being done) or you will take it further. As an annex you can summarise the appalling behaviour of dealer's customer facing person.
As to courtesy car, that is covered under Kia warranty T/C. It is down to dealer.