By your description I Become sure GDFS is damage.
1)When you use from seus and or do any work for flash phone the programme set new value in the gdfs phone so its relative to gdfs.
2)May you dont choose phone in Seus and it update your phone by other frimware.
3)May your phone was change and when you update phone Seue comeback orginal IMEI and the network don know your phone.
4)The best way use backup gdfs