Thank you for the clarification.

OP's statement that he uses a Spanish mobile network in Luxembourg does indeed sound very implausible. Especially because data roaming within the EU is still horrendously expensive and hardly suitable for prolonged use.
Also, with data roaming there is no guarantee that you would even get an IP address of the original (in this case Spanish) network, this heavily depends on the data provider your SIM is registered to when you access the internet.

OP could of course present other documents such as a residence permit, rental contract or registration certificate to prove that he is actually in Luxembourg. However, this raises the question of whether Rollbit would even accept such documents as proof.