Accidental internal calls made might incur huge charges for me | Please help

Hello,

After I travelled back from India on May 26th to the US, I forgot to activate the third party app I use to make international calls and accidentally used the local network to make those calls, and I suspect my charges might exceed 1000 dollars this month. Please help since I'm a student and this is really worrying me. Can you please shift me to the international calling plan, so that the charges can be waived off and included in it?

Regards,

Sourabh