Hi - I'm new to this - I have purchased a $200 pre-paid sim and wondering about calling Croatia. Unfortunately Croatia isn't one of the countries where calls are included so I need to purchase an add-on of $15. I assume this is $15 per month? I'm then wondering what is the cost per phone call? When I search up Croatia on the Boost website, it says calls are 70c - but is this a one off fee? Is there a per-minute charge or a time limit? Thanks.