Asking to serve a non-client company

I am working as Manager in a IT service based company. My company (here fater refer as seller) is acquired by another reputed Indian compnay (here after refer as buyer) but the position offered for me in that compnay is very low. Hence I decided to not accept the offer from the buyer compnay. I have not resigned from the sellecr company also. As per the terms of conditions in the offer letter either partee can break the contract by serving 3 months notice. Now the seller served a notice to me for serving 3 moths and there after my job will be ended. As per the terms and conditions in my sellers offer letter I need to serve only the client of the seller. Since the buyer is not the client of the seller I informed the seller that I am ready to work only on those projects which are executed by either the seller or it's client. Is my stand is leagally right? Can I ask the seller to show documents which shows that the buyer is still a client of the seller, if they force me to serve 3 months for seller? Can I take any legal action?