My brother's iPad 2 will not connect via sim data, now only will connect to internet wirelessly

My brother has had no problem with his iPad 2 connecting to internet with his sim, until the past 10 days or so. I have tried re-setting network setting,restarting, taking sim out and replacing it back into the iPad, but nothing seems to work. When I place my brother's sim into my phone and turn on Portable wi-fi hotspot, his iPad has no problem connecting and being able to use internet.

Please can anyone help here?

(I am sorry I do not have specs for this iPad, but if needed, can get them and detail them here later)

Thanks