Problem Tenant - S21 & S8

Possession - Section 8 and Section 21

I'd be grateful of advice on how to proceed on the matter below.

Situation:
I bought a tenanted property.
Issued the relevant form notifying tenant of change of landlord.
Tenant signed an AST and was issued a S21 on commencement of the AST - both issued by the previous landlord.
Tenancy has been running approx 3 years and is currently a periodic.

As the AST is periodic and a S21 has been issued, can I use the existing S21 and ask the tenant to leave? Or, do I need to issue another one?

The tenant has been asked to remedy damage to the property and has not done so in the specified 2 months. Should we also issue a S8? In addition, on the last inspection he physically removed me from the property - is this a reason that should be stated on the S8 too?

Are there any other factors I should consider as the Tenant is being extremely awkward and I fear he may damage the property before leaving - and the previous managing agent lost the tenant's deposit so we have no recourse without issuing a small claims court claim.

Grateful of you assistance on this matter.

Kerry.