If you still think this is an IMEI issue: I know people fake an IMEI via ASTRO File Manager (Metago) or ES File Explorer File Manager (ED Global) or XPosed IMEI Changer (Vivek.V). You should find all three on Google Play. I think you need to be rooted for all of them. For sure for the Xposed module, for which you also need a modded Android to dock into.

But first, have you tried taking out the 2nd SIM?