Is it actually necessary to use a paid authenticator app? Because why not you use Google authenticator app which could be found on Play Store and Apple Store for your Two factor verification? Because that's actually what I use for securing all my apps for my two factor verifications, and you could also use the same, and stop paying a penny for your Authenticator process. And all you need is just an active Gmail account,  the setup keys and you are good to go. Because since you just changed your password and went ahead to wanting to place a withdrawal, that must have prompted the exchange bot requesting for an extra means of verification. Of which I think Google authenticator app is the best for now.

Here is a screenshot below