Difficult tenant with rent arrears and refusal of access

Rent Arrears

Hello
I have a very difficult aggressive tenant - after he moved in he informed me that he had mental health issues, with arrears of 5.5 months, I am just waiting for it to hit 6 months. He has refused access for inspections, repairs (although he has made a complaint to local council environmental health regarding disrepair) and to carry out an electrical safety inspection. I have applied for a direct rent payment through his UC but this was rejected - I am currently looking onto making an appeal. I have served both a section 21 and will serve a section 8 as soon as I can. What have I missed here? I manage 20 properties and have an excellent relationship with all tenants except this one. Any other advice as I feel like the system is currently stacked against the landlord in these Covid times.