Flat rental deposit return

Good morning.

I have vacated my previous accommodation exactly four months and half ago.

The Estate Agents still haven't refunded my deposit back, in any way, either by check or by bank transfer.

Now, i still need to research and seek for legal advice, but I am pretty sure that an agent has a legal requirement as a dead line for returning a deposit to a tenant.

Would you let me know what is the agent's legal requirement to return a deposit, please? How long should it take? 6 weeks, 8 weeks or more than that?