Is there a way to block certain phone numbers / contacts?
No, I have been using Funamo for 3 years and it does not do it.
Funamo only monitors call and text messages. It does not block them. Many device models already have call/text blocking built-in. For example, all Samsung devices have this feature. If your device model does not support it, you may try some 3rd party apps. Simply search for call blocker on Google Play and you will be able to find many that you can try.