You can't really pay the final months rent from the deposit, this is possibly stated in your contract, but they can not change the locks on the property. It takes up to three months to remove a person from a property through legal channels. Even if you remained in the property not paying rent for two months a landlord has no right to change the locks. Your contract was until May 18th, you gave then no indication you were leaving early, so why then would the landlord assume you had vacated? I think there are contractual breeches on both sides here. I'd advise you contact your local Citizen's Advice

I was paid by cheque. You can request that you are paid in this manner, but be aware that any debt that you have outstanding will remain. It maybe an idea to use this money to clear some of that debt. I know it means not having it in your account, but it's one less debt on your mind.

I had bank charges refunded to the total of £1200 in Jan. since then I have been overdrawn about 5 more times (always by under £10 mind, and usually because of a charge) each time I wrote a letter asking for a break down of the charge. I stated that I am not against fair charges, but I disagree with exoribitant penalties, which is what £28 per transaction is. Each time they either refunded or halved the charges. Until last month where they refused point blank to refund anymore. So I told them that I will again take it to the small claims court. So, yes. Claim again.