Thank you for reaching out and for explaining your situation. I cannot tell you definitively whether you should fulfil this order or not, but there's a few things you can consider before making that decision.
First of all, have you taken a look at the risk analysis for the order? The different billing and shipping addresses could be a potential indicator, but is there anything else mentioned here? One thing I will say is that the billing and shipping addresses being in different countries is certainly suspicious, and could indicate fraud (although there is a chance that there's a perfectly reasonable explanation for it as well). You definitely made the right choice in reaching out to both persons to ask for validation, as quite often illegitimate customers will not respond to any questioning they receive.
The decision on whether to fulfil the order ultimately comes down to you and whether you are happy to take that risk. If you fulfil the order and it turns out to be fraudulent, you will likely receive a chargeback from the cardholder's bank and might well end up without the product(s) and the funds. For this reason, I usually recommend that you cancel and refund an order if you are not sure about it, and would say this is especially wise to do if the customer has not responded to any of your correspondence.
It's always a good idea to be vigilant and take active measures with fraud prevention, reducing the chances of you fulfilling an order that turns out being fraudulent. I'd also say to trust your gut to some degree; if it doesn't feel right, sometimes it's best to trust that instinct and play it safer.
I hope my advice has helped with your decision but if you have more questions please let me know.
Victor | Shopify Social Care
that does sound sketchy - I'd simply cancel the order and move on to spare yourself the potential hassle of dealing with chargebacks. Shopify's risk classification mechanism is usually spot-on when it comes to high risk orders.
We've installed the "Fraud Block" app (https://apps.shopify.com/fraudblock-fraud-prevention), which automatically cancels all high-risk orders - super convenient, since no more fraudulent orders will slip through.