A sulphur bomb might be a good idea if you can get one. Se it off and shut the greenhouse off for 24 hrs. You can also buy sulphur in many fungicides and works brilliantly. The sulphur bomb will help greatly in sterilizing your greenhouse. Implement measures to increase humidity and air flow, a fan maybe. As for the mites they do show widespread resistance to many pesticides so concentrate on purchasing a miticide as mites are not insects. All of the above can be used as a precaution in the future. Forbid 4F miticide 0.5 ml per 2 liter water proved a success for me and showed no phytotoxicity ( bad reaction to chemicals) on my orchids. Continually wipe underside of leaves if possible but remember to not cross infect. Dedication and patience is your key here and you will get there. Mites have given me many nightmares but I know the early signs now so they always lose.