Hello, sorry to hear about the mite infestation they are a pain!!
First things first... check, check, and double check that you have disinfected every nook and crannie in the coop. Under roost bars and in corners of nest boxes are the worst for red mite!
NET-TEX is really good for mite control, i notice your from uk like me. Im not far from manchester. So here are products i would use. The total mite kill ready to use solution is best to squirt all around the coop then use the total mite kill spray (aerosol) to reach nooks and crannies as well as spraying the underside of the roof. This spray is a long lasting control in the hard to reach places. After puttin fresh bedding in put down the total mite kill powder in the coop, on the birds and in the dust bath.
If this doesnt work and you still find your infested, there is an alternitive that is expensive but you know it will work. They are £45 and are called androlis predatory mites. They do not harm you birds or feed off them, they feed off the red mites that live in the coop and on your chickens. You can purchase these from dragonfli.co.uk
If even after that you still have a problem it may be worth investing in a plastic coop if you dont already have one.
Hope this helps good luck, let me know how you get on x
