Hello Josy Menazes,
I would go one step ahead of what (Cite Contribution) mentioned: "The amount sounds exorbitant !".
It's NOT an amount issue at all. It's that this Company just has misplaced notions of what hiring is all about.
Generally every Company which hires thru Agencies/Consultancies have a Standard Clause in their Agreements--called Replacement Guarantee Clause. If the candidate leaves before a specified period of time--for whatever reason(s), then the Agency has to either refund the Fees paid OR give a free replacement. Usually it's 3 months. In your case this either doesn't seem to be there OR has crossed the 3 months timeline where the Agency COULD be refusing to give a replacement.
hence the Company wants YOU to become the scapegoat.
It's BETWEEN the Company & the Agency......none of your business to get into what's essentially a relationship issue between them.
Generally.....at least in the very few instances that we experienced.....the Agency gives a replacement for a lower one-time fee rate for cases that are technically & legally beyond the Replacement Clause effective timeline, but ETHICALLY not really so [after all it's not a large time span/gap between 3 months & 4/5/6/ months].
Coming to 'what to do', since you have the complete situation in writing, suggest inform them THRU WRITING that you are being advised to go legal & put everything that is still only verbal into writing.....basically generating a written record of the complete situation. Going by the general human psychology, the Company would hesitate to move forward, UNLESS they have something against you OR you have not put all the facts here in this posting.
And now coming to ANOTHER ANGLE. Don't you think YOU too are @ fault for resigning so soon after joining? Unless there are very strong reasons to do so? Especially @ your seniority?
Suggest give this a thought.....while technically none can stop you from joining elsewhere whenever you wish to, in the long-run you would be doing your career more damage than good when you jump without strong reasons/justifications in such a fashion.
Rgds,
TS