Other way round. Facebook bought them in 2014, and they dropped the fee in early 2016.
The fee wasn't enforced in many developing countries, and some users elsewhere will have been jumping through the delete-and-reinstall hoops (which was painful because it lost chat history) to avoid paying.
But with 1bn active users at the time the fee was dropped, it would still have been bringing in more than enough revenue to have sustained Whatsapp as an independent business if they had chosen not to sell to FB.
