HTC M8 Sprint 831C signal issue

i have htc m8 harman kardon edition model number 831 c. It doesn't support lte band of Pakistan due to frequency unmatched. to unlock all the frequency of lte band i read some threads in this website and change the nv value of mobile through QXDM and QPST. unfortunately, due to some mistake or by wrong information i have changed the nv values of gsm as well like 0441 etc. i don't know the exact values now, but after this my phone is not picking the signal. it shows circle on signal bar and continues. Aeroplane mode very difficultly switch to on otherwise signal bars remain fluctuating and drain the battery very quickly. i am not able to change network mode by applying *#*#4636#*#*. i have flashed the phone, install custom rom, reinstall software, root the phone but no effect.

Kindly help me i dont want to lose this phone.

waiting for your reply.