Welcome to the community!
Sorry to hear you've incurred unexpected additional charges. Have you had a chance to view the detailed billing to see the particulars of those charges? You can do so via your My Account --> Billing & Payments. From there, you can Save and/or Print a PDF copy of your bill. Alternatively, you should also be able to view the details online under Other charges and credits (see here).
Are you aware that those 1000 International minutes are only to certain Countries? You can view the included Countries (see here).
In addition, you should note that all calls using mobile services incur Airtime charges plus long-distance charges, if applicable. Those 1000 International minutes are only for the long-distance portion of calls. That is, airtime charges would still apply. If you have a plan with a limited number of airtime calling minutes, excess airtime usage would incur additional costs -- even though there may be available International minutes remaining. For example, if you had a plan with 500 Canada-wide minutes (airtime minutes), making 600 minutes of calls to Countries included in those 1000 International minutes would require an excess usage of 100 airtime minutes. Is it possible you exceeded your airtime minutes?
You should also note that these forums are community-driven and not intended as a venue for customer services. As such, we do not have access to customer accounts. If you would like to discuss those specific charges, you would need to contact customer service. In addition, they can also be contacted via Live Chat, Facebook, or Twitter. Those methods can be accessed via the contact page posted above.
Hope this helps 😀