One more comment about the “two non-contradictory pieces of evidence”. They may not be available, and that should not be an issue.

Example
– The billing address of the customer. This is available and declared by the customer. If he lies, that should not be our problem.
– The Internet Protocol (IP) address of the device used by the customer. This information is unreliable. If either your site or your customer use a proxy, the IP address will be incorrect. Proxies and VPNs are getting more common (e.g. use Hola and your location magically becomes another one), so we can’t really rely on the IP address.
– Location of the bank. We may not have this information. If customers pay via PayPal, or other processors, there’s no way to find it out.
– The country code of SIM card used by the customer. Even more uncommon.
– The location of the customer’s fixed land line through which the service is supplied to him. This is even more uncommon than the SIM. What services are supplied via a landline, apart from broadband and telephone?
– Other commercially relevant information (for example, product coding information which electronically links the sale to a particular jurisdiction). Product coding can be arbitrary and generated dynamically, it’s not a reliable piece of information.

This boils down to what I was telling to my accountant: the billing address is the only one that may be relied upon. It’s declared by the customer and we must take it at face value. If customer lies, then he should be responsible for the consequences.