Replying to nightscavenger - I was not using the same substrate that was already infested with mites, it was unused, and I left that opened bag of substrate in the garage for about 2 months, so any mites should have died by then.
And the spray might be the problem, maybe I need to apply it more times, but callingtons is quite a well known brand in the uk so it should work. Also mite hitchhikers is a good suggestion, however I can't really help going into a reptile shop as it is the only one nearby that sells frozen rats