OnePlus India — thane mumbai service center did not fix my oneplus 3t issue

Address:

Lake City Mall, G-4, Kapurbawdi Flyover, Majiwada, Thane, Maharashtra 400601, Thane, Maharashtra, 421204

People at the "lake city mall, g-4, kapurbawdi flyover, majiwada, thane, maharashtra 400601" service center are very unprofessional. They wasted my time and money and i got nothing but disappointment.

I purchased my oneplus 3t phone in usa. When i came back to india realized that 4g services are not working on my phone. I called these service center people and they said, come to our center, we will fix it.
I traveled 25 km and visited service center and they said ; sorry, we can't fix this because your imei number does not belong to india. Such an irresponsible reply. It was pretty clear that the imei number would belong to usa if i purchased it there. Alternatively they could ask me to provide imei number over phone when i first called them.

If oneplus has any way to open up indian 4g bands on my phone then please do it. I am having so much trouble with the network.