My ex-boss has held my relieving letter

I recently left a job because of toxic workplace. I survived seven years (yes, 7 years) there and it was toxic af. The team is full of under qualified mediocres who are ready to lick my boss' feet 24*7 (even till personal level)...I had enough of it and decided to quit.

Even during my notice period there was a lot of drama and false allegations that I did not give any handover to the team. I escalated it and looped in my HR with all evidences.

Now since I have left, they hired two more people as my replacement but still badly stuck (which they deserve).

My relieving letter is stuck because my boss refused to sign my no-dues because of her ego.