Rent Arrears after Bed Bugs

Rent Arrears

I have a flat that had a bed bug problem in September of this year. I immediately got an exterminator in to chemically spray every bedroom and the lounge in the flat at cost of £420. The tenants had to wash all of their clothes in the washing machine at high temperature and then keep their newly washed clothes in black "clean bags" for two weeks until the next treatment. A second chemical treatment was undertaken by the exterminator, however, two tenants left the flat because of the bed bugs. As a result those rooms had no occupant and the exterminator advised that without occupants in the bedrooms, bed bugs would not feed and wouldn't climb over surfaces with the insecticide. Therefore the treatment would likely be unsuccessful. As a result I undertook a heat treatment, at a cost of £1200, that killed the bed bugs immediately. Two of my tenants who were present during the chemical and heat treatments, have refused to pay rent for the entire month, citing the anxiety and mental health issues caused by the bed bugs, and the inconvenience of having to live with their clothes in bags etc. The infestation was not there when the tenants moved so was brought in by one of the current tenants. I'm happy to provide a discount to these two tenants for the inconvenience, having offered 30% off, however they seem unprepared to pay anything for the month. How am I best to proceed to encourage further payment without them citing "harassment"?

Thanks & Regards,