Landlords and tenants both must follow the correct process to end a tenancy. You can end up in court if you, or your agent, do not follow this process.
The deposit belongs to your tenant and you must return this at the end of the tenancy. You may be able to keep some of the deposit, if you can prove that the tenants owe you money for rent, damage or cleaning.
You need to get a court order from a county court to evict a tenant who does not want to leave. You can also recover rent arrears or compensation separately through small claims court.