Deposit:Managing Agent being difficult and holding deposit

Tenancy Deposits

Hi All, just some background, I'm struggling with the Managing Agent who was looking after one property where the tenant had to be evicted for not paying rent (over a years worth of rent not paid).
The eviction has taken place BUT the tenant left belongings there. I have had an Inventory Check out performed on the day of eviction as the Managing Agent initially refused to do so the same day siting issues e.g. the eviction may not take place. They have been constantly difficult and have thrown obstacles my way constantly ie. not sending the formal letter to the tenant to as him to lawfully collect his belongings, refusing to accept the Check out report as they didnt complete it etc etc.
Long story short is whether the Managing Agent can deduct 'outstanding fees' from the deposit that they are holding and insured via the TDS + what is the legal stance on asking me to sign indemnities for taking the deposit (less their fees) for either the outstanding rent or for dilapidations. I've never heard anything like it. I've been given advice to raise a formal complaint by the Property Ombudsman but does anyone understand the legalities of deducting fees from a deposit and signing indemnities!!