Contact customer support via the links supplied by @dabr and ask the CSA to remove the international add on and change it for the US calling add on or ask for a credit to your account. You can also try downloading fongo or textnow and choose a Canadian phone number to the US for free while on wifi or mobile data.
@maikolsolis Sounds like you purchased the wrong add-on. You need to purchase 1000 US mins/$15 add-on instead and if you don't need the 300 international mins for future use, then message customer support and see if they will credit back the cost (as long as it's unused) for it.
Here's couple of links to support, try chatbot first.
