Where are you travelling to? Was it the US? If you traveled to US, you are automatically entitled to roaming without any add on. 
anyway, among the add-on , the volte access wasn’t a roaming add on. It is a helpful add on to allow you access volte. I suggest you keep it.

If you don’t want to roam, you could also put the phone on airplane mode (or take the SIM out)

If you want to receive texts, you need to keep the International Voice Roaming add-on. Otherwise, you will not be able to. It is free to receive them. You will only be charged if you send out texts.

As for voicemails, you would not be affected, as long as you do not make any calls while abroad. 

Are you able to log on to your Self-Serve account? You only need to remove the International Data Roaming add-on to avoid any unexpected data overages.