It is felt that the statements of line management/HR are verbal. Company may cite standing orders if applicable to your industry.
First of all you should settle with new employer by explaining the facts and later preferably in writing.
Your current employer may not agree to notice pay and may not issue acceptance of resignation/relieving letter/work experience-service certificate/form 16/FNF statement.
In such a situation it is imp. to take new employer in confidence and obtain concurrence to absorb you on the strength of copy of notice of resignation, final resignation, and POD. You may communicate with current employer by email followed by letter thru redg/speed post only.
You may submit a notice of resignation with effective date of resignation/last day in office addressed to the good offices of your appointing authority, MD, CEO, Company Secretary with a copy to Head-HR. If you have already submitted notice of resignation you may submit a written representation addressed to the good offices and mention the date and date of submission of your notice and narrate that as per clause no.........in appointment letter dated.............issued to you ............the notice period of resignation is ..........days and you have complied to this clause. On dated..............Mr/Ms..........designation.......dept............address.............has asked you in office, to serve notice period for 3 months which is against the terms and conditions expressed in your appointment letter. Company has never supplied any communication regarding change in notice period to you in writing and you have never given your acceptance in writing. Hence you are seeking intervention of good offices and relief and a written acknowledgment of your notice and acceptance of last day in office as dated...........as expressed in your notice dated...........You may request the good offices to ensure smooth exit formalities and to supply you the acceptance of resignation/relieving letter/work experience-service certificate/form 16/FNF statement, payment of your dues by bank DD,NOC/NDC,PF number, attested copies of PF withdrawal/transfer forms etc within your last day in office i.e./ dated............You may mention that good offices may inform you in writing to whom you should handover the charge and company property and employee designated may be advised with a copy to you, to issue acknowledgment and routine work may be assigned to you on in routine which can be completed within your last day in office. If you are eligible you may submit form I for payment of gratuity under proper acknowledgment.
You may forward/print copies of all relevant emails, appraisals, and performance/incentives data.
Employee can seek relief under enactments like Industrial Employment Standing Orders Act, SE act applicable to your state, Industrial Dispute Act, as per explanation of employee under these enactments. You may approach a competent and experienced service lawyer and show all records and proceed under expert advice.