regular teacher breach of contract

hi, been working as regular employee in this school for 10 years as a high school teacher. I decided to resign to work in an IT company.
date of resignation(nov28)
effectivity ( jan2).

content of contract:
" This contract automatically terminates by the expiration of the term unless renewed at the option of the FIRST PARTY. However, the FIRST PARTY may pre terminate this contract, upon a one-month notice in writing, in the event of any breach of any conditions hereof by the SECOND Party. If the SECOND party for any reason wish to leave at any time before the expiration of the period agreed upon this contract, the SECOND party shall pay the FIrst party, the sum of the monthly salary corresponding to the unexpired period of this contract.


questions:

1. is it legal to offset my 13th month pay and december pay in exchange of my contract price without due process?
2.if yes, what else can i do to prevent this from happenning?
3. are there other ways i can counter attack the management to force them to give my 13th month and december pay?
4. under education law, are teacher's contract substantial to collect money from the resigning teacher even if she is a regular employee?

you can file a money claim at nlrc, and it has the power to decide whether the contract is valid.