Recently a friend who is a landlord had a tenant pick up and leave without pay a few months rent. The landlord had unfortunately misplaced the original signed contract
If the tenant has paid X amount per month for a while and then that amount has not been paid for a few months this adequates proof of a contract.
If the Tenant wanted to leave then he/she would need to prove he/her gave notice to the landlord to end the Contract
Write the person a letter to his registered Office ,this can be found online at the companies house https://www.gov.uk/government/organisations/companies-house
Explain why he owes you the money
What evidence you have ( the letter acknowledging he owes you is all you need )
Attach that letter and give the person 10 working days to make the payment to your account ( Include details )
Explain you have sought Legal Advice and if he/she fails to pay you , you will take legal action against him
Send this Recorded Delivery to have she/he has signed for it
Once the 10 days is up , submit a small claims court against the company for the amount
Can be done here : https://www.gov.uk/make-money-claim
The court will Issue a CCJ on the defendant which he can choose to pay , pay in installments , rejects or counter
If you he ignores, you can enforce its judgment – this will incur more costs and could even extend to bailiffs visiting you.