If you have sent a clear mail for disconnection, you are not liable.
You may log in to website of the company and obtain email id of VP-Legal, Company Secretary, MD/CEO, and forward the email with comments company employees are engaged in illegal activities of issuing thread to you/coercion/harassment ( mention the phone number, date time, name of calling person) and company should at once stop phone calls and issue a letter to you on its letterhead, under original seal and signature, that it had received your instructions and phone connection has been disconnected and all bills are paid and there is no outstanding and if company has included your name in list of defaulters and passed it on to any of the collection/recovery agencies ,credit bureaus it has been withdrawn and thus in future there shall be no negative bearing on you. If there is any adverse affect on your credibility company shall be responsible.
You may visit the company’s local RO in your city and represent to Regional Head, with a letter ( same matter as supplied to VP-Legal, Company Secretary, MD/CEO), obtain acknowledgment from them, and their phone number email id and later submit minutes of your discussion with them.
Next time if any one calls you, you may record the phone call, ask the calling person to speak his/her name with sir name, designation, name of company/agency, its address. Thereafter you may issue reminder to VP-Legal, Company Secretary, MD/CEO, and mention that you have represented to Regional Head, and you shall be constrained to lodge a criminal complaint and approach media, if company does not supply you the letter by registered post and refund of your security with interest, so as to reach say within next 7 days.
As per TRAI Rules, Company has to pay interest on security deposit after stipulated time.
You may in fact lodge a complaint with Police commissioner, SHO of your area and mention that persons calling from phone numbers, and RO of company ( give names), are impersonating as Police official/court officials, and threatening to cause you physical harm, and obtain acknowledgment/complaint number. Let the police call RO staff.
Companies claim that customer has to visit company’s office for disconnection, and obtain FNF payment receipt. You may go thru the terms and conditions mentioned in SEF submitted by you and be ready with your defense.