sgs4 sim problem

SIM problem with i9505
I have an s4 which was on Tmobile, i upgraded in a shop to a note 3 om EE and had my number ported to the note 3, ever since the s4 will not take an EE sim card, it just says there is no sim inserted, strangely though there is signal showing but when you try to dial out it says not registered on network, i have spoken to Tmobile, EE and taken it into numerous shops, essentially they are useless and dont want to know, i dont think the SIM socket is damaged as it takes every other sim and works fine. I just flashed an EE stock firmware to it but still it doesnt seem to accept the EE sim.

I have also put root checker on the phone which is saying the unit is not rooted properly, if that is so then surely i wouldnt have been able to flash the firmware to it ?.

Not sure what steps i should take now to try to sort this out, the carrier is denying that the problem was caused by them, some have said that it is locked from the EE network, if that was so i would have no service, not an uninserted sim error.

Is there something that will unlock it if indeed it is a lock problem (which i dont think it is)