To be fair, there was never any argument from Glasses Direct, and they have been very pleasant on the phone, despite all this hassle. I have also heard good things from other people about them, so I am willing to believe that I have just been extremely unlucky.
At long last, my varifocals have arrived from Glasses Direct. This is the third pair I have had from them, having returned the previous two due to problems with the frames. Similarly, my sunglasses had to go back the first time, due to the left and right polarised lenses being aligned differently.