Help Device not falling back to 3G from 4G

[theflyingrahul]

Hi,
I have a Lenovo vibe k6 note stock rom on Android 7.0.
Calls are working perfectly in Jio 4G (volte).
Recently I switched to Vodafone 4G (no volte).
When I try to place calls, the device is not falling back to 3G. I am unable to switch the network to 3G or 2G manually also. However 2G works when I change my primary data Sim.
I tried swapping the sim slots, toggling enhanced 4G services, restoring the device software, changing sim cards, replacing my sim card, the same problem persists.
I am using this sim with Lumia 640 XL LTE now. This issue is not present with other phones.
Any help would be appreciated.

 

[lvt]

Do you mean you are using your Lenovo as hotspot and when you are making calls, there is no Internet connection?

 

[theflyingrahul]

No, data works perfectly.
I am not able to place any calls.
On a non-volte network, the network falls back to 3g from 4g when placing calls right?
In my case I am not able to place any calls as the network is not falling back to 3g.
Thus when I try to make a call, the call disconnects immediately.
I think I am facing this issue only after unlocking the bootloader, I am not sure though.

 

[lvt]

Unlocking the boot loader usually doesn't stop you from making calls, unless you carrier did that on purpose.

 

[theflyingrahul]

I tried to relock the bootloader, still no luck!