Netgear MR5200 'Mobile broadband disconnected'

Hi all,

I have two Netgear MR5200's, after a couple of months with my first I received the message 'mobile broadband disconnected'. I was using an EE sim, I tried various sim cards in the device and played with the APN settings but to no avail. I contacted Netgear and received a replacement device, which worked for around 8 months (I even checked all the firmware/hardware details which were identical to the first) but now it's come up with the same issue. 

Firmware version: NTGX55_12.04.17.00

Hardware version: 1.2 

Any help would be greatly appreciated