No use in trying any other hack, as the problem is bad coverage of band 40 in your area. Even if you make your opo to work with jio Sim, the coverage issue will persist. Because by default in Jio networks 2300MHz will be used if available, then priority to band 3 and finally band 5. If you are getting 850MHz signal only, it means the signal of other bands are very weak.
I can give you one better idea. Just find out one spot mostly near window or door, where you get weak band 40 signal and keep your phone there and use Wi-Fi tethering.
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