Samsung Galaxy 4s not recognising Three (3) network sim card

A

AC Question

I'm currently 7 months through my 24 month contract and have bought an unlocked Galaxy s4 for the contract sim.
However the phone won't recognise the sim card, it only allows me to make emergency calls.
The phone recognises sim cards from other networks such as 02, vodafone, and giffgaff, but I've even bought a replacement 3 sim card which the phone is still unable to recognise.

Could the phone be only partially unlocked?
If so, how do I fix it?
It could well be another issue, any suggestions on how to fix this would be greatly appreciated.
 

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