Thanks for your question. I hope I can be of assistance to you.
Firstly, was the deposit registered in a deposit protection scheme (tds)?
If yes, it must be repaid within 10 calendar days of the end of the tenancy. The landlord is entitled to make deductions for cleaning, repairing, decorating and clearing any rent arrears.
It is assumed here that the landlord has agreed to repay the deposit in full. Do you have any email or other written correspondence from the landlord regarding this? I.e anything to say that the landlord intends to refund the deposit in full but has spent it, only repaid part and your offer that they pay £100 installments? I note you have emailed, do you have any replies from the landlord?
If the deposit was registered with a tds then you can make a complaint to the tds. The tds can suggest mediation but the landlord does not have to agree. If the landlord does not agree then the tds cannot help and you will have to go to court.
At this point I should mention that if the landlord did not register your deposit with a tds then the landlord may be liable to pay compensation of between one and three times the amount of the deposit.
Going to court, the value of your claim means you will make a claim with the small claims court. This is done online at money claim online. For this you will need your documentary evidence and you will set out your claim, you will state what you are owed and whether or not the deposit was registered with a tds and claim that the court should award compensation if not registered with the tds. You can claim interest. Check your tenancy agreement to see what it says, if silent you can claim the statutory interest of 8%. Here you claim the amount in full plus interest.
You will have to pay a claim fee but this will be added to the claim, the court will do this.
From here, court will issue the claim. The landlord will have a specified period within which to respond either (1) admitting claim (2) defending it, I.e the amount withheld are allowable deductions for cleaning, repairing, decorating and / or covering unpaid rent.
If the landlord does not admit /defend within the specified time then you will have judgment in default (jd). If landlord admits or jd the court will make an order. This could be lump sum, installments.
If the landlord still does not pay you will then have to return to enforce the debt.
If tds protected you can still go straight to court and bypass tds.
I hope you recover the money owed. Extremely irresponsible of the landlord to spend your money (deposit money was yours, they only held it on trust).
I hope the above is helpful. Do let me know if you have any questions or queries in respect of my answer.
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