You still have an AST, you can prove how long you lived in the property with bills, electoral role, Council tax etc.
If there was an unfair term in the tenancy you would use Unfair Terms in Consumer Contracts Regulations 1999 to take any action.
Your money must have been put in a rent deposit scheme if your tenancy started after 6th April 2007
https://www.gov.uk/deposit-protection-schemes-and-landlordsOtherwise you can he evicted with 2 months notice, but currently 3 months notice due to Coronavirus. Courts aren't currently doing evictions.
If you deposit should have been put in a rent deposit scheme but wasn't you can claim 3xthe about in compensation.