Learned experts/members have given valuable advice. Kindly follow it.
Apparently you have not submitted any joining report and the company has not mentioned in any of the communications sent by it that if the candidate does not join after acceptance of offer the candidate shall be liable to pay amounts……towards say…expenses incurred by it?
The HR personnel are expected to ensure joining of selected candidates and are usually chased by their seniors and it might be part of their KRA’s. Hence the chase.
If you feel you may sooth them on phone or in person and let the bubbles precipitate.
Although you have mentioned that it is appointment letter. Still you may confirm if it is appointment letter or offer letter making an offer of appointment in month of April?
If it is offer letter you can decline after reconsidering your options and reasons.
The HR/company may at the most stake a claim for notice pay from you, based on the contents of the letter issued to you.
However you may check in the appointment letter issued to you the notice period/pay mentioned in it, pertaining to training/probation period and after confirmation and that post offered is temporary or permanent.
If standing orders are applicable to the company then appointment letter has to be in line with certified standing orders of the company/model standing orders.
Model Standing Orders:
13. Termination of employment: notice period is not applicable in case of temporary, probationer….
If establishment is covered under SE Act:
e.g. SE Act Delhi:
30. Notice of Dismissal: if service is less then 3 months no notice period is required.
Did the company allow you to examine the offer/appointment letter for sufficient time say….a day or two? Or did it ask you to sign it on the spot, then and there?
You may also check for certain negative covenants in the letter e.g. service agreement, non compete clauses, and choose a reason suitable to decline and thus put the matter on a “Shut Up mode.”
If you are perturbed or are being disturbed approach your lawyer and your lawyer shall do the needful.