Vivian - It's time for you to handle circumstance a li'l different rather to bemoan about the present employer. Since you are done serving the notice period, you've all rights to inquest on your releiving process -- Write a letter and an email (elucidating your condition -- also add that you do not have any pending works to complete) addressed to the HR, HOD, Management personnel's updating that your NP has been served & request them to releive you with the F&F at the earliest. Keep a copy marked to your personal email for any further correspondance.
Await for a day and if you do not get any response, share the email copy with the New Employer (that you're being bullied by the management) seeking their approval to join as usual. [See what they have to say]. In case, IF the present employer does not act in response to your case; you may seek a labour comissioner's office with all the documents (appointment, resignation letter, copy of an email provided recently enquiring releiving), an application from a conciliation officer will have all your problem solved. This method is MODEST and employees do follow modus operandi for a better future.
I understand that the New employer will watch over the part before it takes time for thsi process. Before all this, set things with your new company and then "+" your step. Self-confidence should be your biggest tool.
Self help is the Best help!