1) in probation period company can terminate without assigning any reason, but for that appointment letter must contain such a clause
2) in case you have agreed that in the event you resign during probation period you shall pay 3 months salary it would be binding upon you
3) For unpaid salary, approach the Labour Commissioner who will help re-concile this matter with the company. If no solution is reached, the Commissioner will hand over the matter to the Court, whereby the employee can make an application to the Labour Court under Section 33 (C) of the Industrial Dispute Act, 1947.