Tenant looking for compensation re damp

Maintenance

Please can you help?
We have just received a solicitors letter relating to a complaint from one of our tenants about damp in our property and would like some advice please. They are claiming that we are bad landlords and have done nothing to fix all of the damp issues with the property, however we have sought help and advice from numerous damp experts and the environmental health and all say the damp is being caused by their lifestyle not us. The advise was that the house needed to be ventilated, which they told us that the tenants need to open windows more and put the heating on however the tenants are saying we as landlords should be installing a state of the art ventilation system. We fixed the guttering when they moved in which we were told was the cause of a small damp patch, we are awaiting a date to start to get one wall damp proofed and are currently paying to change a fan in the bathroom because the one they use only goes on when the lights on and they won't leave the light on or open the window. But now they are wanting compensation for illness.
The house was inspected and fully accredited by the council before they moved in so we know that lots of the minor things they want improving are not necessary however the things we know are important to do, we try to do but we struggle to get done due to the tenants never answering calls or the door to us or workmen and it is very difficult to gain access to the property to fix the the issues. We have instructed damp companies to give us quotes and help us solve it but we can't get a clear answer from anybody. They all say 'the property may benefit from' or this may be a solution but there is no clear info. We own lots of properties, we take pride in our houses and work closely with the council with regards to accreditation. We do not have the qualifications surrounding damp so have took our advice from the experts. Do they have a case and what do we need to do to ensure that we protect ourselves? We look forward to hearing from you on this matter.
Regards
Shirleyann