I presume you mean that the company itself has been bought out and that you are still employed by the same limited company? But that it now has different owners? In that case TUPE does not apply but existing contractual terms, written or unwritten, still apply and you are under no obligation to sign a new contract. The reality of course is that you should engage with the new owners and see if something can be agreed that suits what both sides. If you refuse to sign the contract the new owners would only be able to make you redundant if a genuine redundancy existed.