Deposit Dispute

Tenancy Deposits

Can anyone let me know if there is a time frame for either party to bring up a dispute for the return of the deposit when the tenants have already vacated. Tenants were in the property 2years, left with rent arrears and substantial damage, left no forwarding address, we located their new address and wrote to them which they ignored, but just before the deposit was due to be released they say they are issuing legal proceedings. This is an idle threat and delaying tactic. The DPS say there is no time frame and the TDS say it is three months. Can you help??