What are potential causes of internet malfunction?
Possible causes of SIM Card and Mobile Data related internet problems,    


Incorrect Mobile Service Provider.
Dirty or Scratched SIM Terminals.
Misaligned SIM in SIM Slot, usually caused by cutting your own SIM Card into a Micro SIM.
Broken SIM Card.
Broken Device Aerial.
Incompatible SIM Slot ( Micro, Nano ).
Incompatible SIM Frequencies, usually caused by having an old 2G Sim card with newer 4G device's.
Mobile Phone Number Inspection, A possible DOS or Denial Of Service may be happening for a specific phone number only.


Without further information I am unable to answer you with regards to your specific problem, 

Try additional information, 
What was happening prior to the issue ? ..
Did you get a new device because of internet issues ( maybe it wasn't the device but the actual SIM Card is damaged ) 

Did it ever work at all, Can you Read SIM Contacts ( Therefore Connect to the SIM )