AirCard 810

I bought the Aircard 810 Mobile Hotspot in early August. I have a contract with the Belgian provider Orange (10 Gb per month included) and have first used the AirCard 810 at the beginning of August in Portugal. This was considered under the regulations for roaming within the EU, meaning the same terms and conditions apply as when using Orange's telecom and internet services in Belgium. I put my simcard from my phone (an old fashioned dumphone, not a smartphone) in the Netgear 810 and when using it in Portugal, NO DATA USAGE was deducted from my 10 GB monthly allowance.

Once back in Belgium early October, the problems started. After 10 days (at the most) into my monthly paying period, i get a message from Orange that my full 10 GB allowance has been used up.

How is this possible?

Why is it that in Belgium data usage is being deducted from my 10 GB monthly allowance, whereas this is not the case when roaming in Portugal?

Is it possible this has something to do with the fact that when in Portugal, I was using the simcard of my mobile phone in the Netgear 810, whereas in Belgium I started to use a "Surf Extra Card" (name used by my provider Orange)? The Surf Extra Card is a second simcard (with another number) connected to the same contract.

Please help me to solve this mystery.

Thanks for your help.

Liesbeth