A contract is legally binding until a new contract is signed.

Till signed all the old terms and conditions apply.

The company can choose to terminate you by giving you the notice in your current contract if you don't sign a new contract.

The term management reserve the rights to amend certain terms of the contract is still valid. However if they need you to sign a new contract for their amendments then the amendments needs your consent before being put in force. And in no terms can they withold your salary unless you owe monies under contract to the company.

If I were you I will fight it out. They will give in if they cant justify. You can also walkaway from the company (due to breach of contract if they don't pay you) without serving a notice period (never heard of this being done in Malaysia before----but I would do it) or you can sue company to get whats owed to you.