Tenant withholding rent

Rent Arrears

Tenant is withholding rent as she is complaining that there is mould in the property. There is no mould or damp in the property. Environment Health Officer has visited the property and confirmed this. Landlord has addressed a variety of maintenance issues since the Tenancy began in August 2021. These jobs include works to block any drafts from windows and doors and replacing all the radiators. Both these were not essesntial works but carried out to improve the property for the Tenant. All issues have been dealt with in a timely and professional manner. Tenant is abusive and rude to contractors, agent and Landlord.
Rent has been paid on time until it was due this month on 16/12/21. Tenant has confirmed that she won't pay the rent until the mould issue is dealt with - there is no mould issue - what can we do?