Deposit not paid back

I rented an apartment managed by rental pros I gave in my 20 working days notice as per the CPA. I vacated the property in question on the 3/04/2022 to date I still haven't received my deposit. I sent an email and was advised that the deposit is used for April's rent whilst there was a tenant how moved in April. They collected rent from that tenant and want to collect rent from me as well which is *********. I asked them which part of the CPA states that I must pay for Aprils rent and have received no feedback to date. They think they are above the law. Instead they sent me letter stating that I owe them for maintenance that they did after I moved out. Which also included fair wear and tear which should be for the landlords account. I don't understand why they collect deposits if they can't pay them back. I will be taking this legally if I dont get my deposit back and I'll also ensure that they liable for those legal costs as it was supposed to be paid 14 days after I moved out.