Do you have new employment letter under the new company?

I think if the new spin off has a new employment letter, and the old one ceases to be valid, then only you may have potential to avoid the bond tenure. Disclaimer : IANAL

You say hypothetical situation, then say the company sold last year. Which is it?

Anyway, your payslip coming under the old company name, or new company name? If old company, only the equity of the old company was sold, and your bond is still valid. If payslip under new company name, then the bond may be invalidated.

So I think your bond contract is still valid right now should you want to change to a new company. As for how to nullify it... sorry la, I can wish you good luck only