I will ask our payment service provider about this, just in case, but from I could look up, you used a completely different card in October. That card was issued by a different bank than the ones you use now, so it's possible that while the previous bank didn't charge extra for international payments, these do. I will get back to you in case the issue originated on our end, but at first glance it doesn't look that way.
The best way to avoid extra charges is to use PayPal, by sending funds to a PayPal account beforehand. I honestly don't know if using a credit card through PayPal will let you avoid such charges, though. It's possible, but it's still a credit card payment, and is therefore subject to all sorts of limitations specific to that payment method.