Record the calls/meetings (audio/visual) especially when he states that “He Forgot”……………..
Don’t remain entangled with these HR personnel. He is not your employer and is just another employee in the company like you.
As per some internal policy of employer for him, he won’t issue the Service Certificate and also relieving letter.
Relieving letter is issued post all settlements by employee. Since there is nothing pending against you and you have even paid the liquidated damages stated in BOND (without consulting your lawyer and assessing these are payable or not) and has served even 10 days more than notice period of 90 days ( without consulting your lawyer and assessing whether 90 days notice period is applicable in your case or not ) nothing is pending at your end.
If during employment no adverse comment, stinker, notice, show cause notice has been issued to you then HR can not post adverse comments against you.
You may first record then minute all discussions with HR (mention phone numbers, dates, brief minutes etc) and escalate to good offices of appointing authority, MD etc…………………………and let your representations be structured by your lawyer……………………….and include that you were coerced/forced to pay and Experience Certificate was dangled at you.
Exhaust the internal options...................................and build irrefutable written record.
Later you can pull them to appropriate forum at appropriate time under expert guidance of your lawyer.
Your lawyer may opine that liquidated damages were not applicable/pro rated damages should have been paid.
There are many threads that you may find relevant and you can pick up relevant points e.g;
https://www.lawyersclubindia.com/experts/Payment-of-indemnity-bond-419196.asp#.UiNgTNKAqWM
https://www.lawyersclubindia.com/forum/Whether-notice-period-has-to-be-given-during-probation-91808.asp#.UwDFP0eBmXU