New to red mite... Please help!?!?

Hi there still new to chickens, have had them for over a month now. Bought my coop off eBay, and before putting chickens in I cleaned it and got in it with a blow torch round all the cracks and perches. 2 weeks after getting my 3 hens which were 18 weeks old, my dad bought me a new hen which was 18 months old, only yesterday I noticed 2 or 3 little bugs on perches which were bright red, 1 guess it was red mite. Today I have emptied the coop, thoroughly cleaned it, blow torched it, sprayed it with poultry shield, then went round with diatom and fresh bedding. I don't know what else I can do. I keep the coop really clean. I am really worried about a red mite infestation. Any advise on what to do to keep them away? Oh and I hadn't first egg today, very happy about that