Block SIM in LG X Power

Hi everyone, sorry I'm writting in english bit muy german isn't that's good.

Muchas brother Was using this LG X Power with an O2 Card for months and everithing was fine.

A week ago, he got a new phone and installed his old SIM card información ir and ir worked fine again.

But, and here Is the problem, when i put MY NEW O2 SIM card on his old phone (LG X Power) it inmediatly said "blocked Voice and Data Services."

And then it gets weirder, my NEW SIM card works on his new phone. But my SIM card and HIS SIM card aren't working on the old phone.

Can someone explain me why Is this hapenning. Does the LG phone Is blocked now???

And how can I fix it???