@Eva_07807 Hello there, welcome to 3Community. Let's take a look at this. Tell me, are you a Prepay or Bill Pay customer? There may be some boosters you can apply to your account for roaming so let me know. Also, where are you noticing the charges? Calls, texts, data usage?
Turning off your voicemail (check out All About: Voicemail for instructions) and disabling data roaming are two things you could do. Let me know the answers to the above questions too and we'll go from there 👌