Short answer: you probably can't. I'm sure there's something in the legalese in the Terms of Service about how they are able to sell the company. Technically Moves still owns the data, but they are now owned by Facebook, so I'm sure they reserved the right to sell their company.
The only way I can think of is if you can find a service that has a legally-binding promise to notify you with ample time to terminate your account and remove your data before merging with another company. But I'd be shocked if many/any companies do this, because they'd be hamstringing their value.
Actually, there isn’t anything in that (kind of) contract other than the fact that the contract is with the company (Moves Oy, WhatApp Ltd.) If Facebook buys out that company, then the contract is the same, but with a subsidiary.
Even promisses to destroy in the contract wouldn’t be enough — because the entity that would promise to delete your data wouldn’t exist as soon as there is a legally binding event.
At the moment, the only thing protecting you from that are competition authorities. If you can file a request for consideration saying that this would harm their users overall (not just isolate case: Competition authorities deal with economic policy, not individual cases), then you might block the overall sale.
As someone who’s digged for years into current principles, I can say taht we are not even remotely close to having proper understanding by the lawyers of what kind of harm is at stake, let alone measuring it; from there, wait ten years and a couple of controversial cases to make it into effective policy.
The only way I can think of is if you can find a service that has a legally-binding promise to notify you with ample time to terminate your account and remove your data before merging with another company. But I'd be shocked if many/any companies do this, because they'd be hamstringing their value.