Please help! No 3G or GSM, can't call, but LTE works fine.

I really need help with my device, I searched all over XDA and no-one seems to have the same issue as me.
Here is some information:
1) Nexus 6P (H1511)
2) 6.0.1 Absolute stock, no rom, no root, no custom recovery. Build number MMB29P.

Recently got a new Nexus 6P and imported to Russia. All of the major bands here are supported. And the phone worked excellent for a few weeks, but then it lost all 3G or GSM connectivity. Just randomly,didn't do anything with it, the only thing I did is move to another city but than I got back, the issue didn't resolve. LTE works perfectly but can't call or receive calls, can receive sms though. Reseting network settings and factory reset changed nothing. Tried manualy set network to WCDMA or GSM with *#*#4636#*#* command, the moment I switch to anything besides LTE the connection is lost. Contacted the provider, no problem on their side, my SIM works good in other phones, my phone with other SIMs - no.

I don't think it is a hardware issue because a few times I managed to get everything working after an hour of switching networks and bands with no particular order in the *#*#4636#*#* testing mode.

After a while I figured that if I set phone to "GSM only" on USA bands in testing mode, but at the same time set it to "LTE prefered" in the normal network settings menu. I am able to set phone to Band mode 7 and set the network back to 2G in network settings keeping it on " GSM only" the whole time and only after this compicated algorithm and after a reboot 2G and 3G starts working. But any reboot after that revertes everything back to only LTE stage. Also if I get everything working but than reset network settings everything stops working again.

I have no idea what caused such an issue, I really hope someone can help.
Sorry couldn't post screenshots because of the "10 posts rule".

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Unable to playback recorded call

Hello everyone.......This is the first time I am posting on any form...So, pls forgive me if i am wrong in any way... I hope any of u cud help or guide me in solving my android problem

I use a Samsung Galaxy Grand Duos GT i9082 mobile....(CPU/Processor-Bradcom BCM 28155/ARM cortex-A9, Processor clock/core-1200 Mhz 32 bit dual core)

Post rooting of phone, I've tried two ROMs (1) AOSP CM 12 5.1.1. Lollipop ROM and (2) AICP 10.1 Lollipop ROM ...... But both have the same problem of playing back the recorded call.... The issue is as below : -

In the first case, there is no option to enable call recording. For that, I enabled CM settings through Xposed installer and downloaded and enabled the module...But, THE CALL IS GETTING RECORDED, BUT WHEN I TRY TO PLAY, IT JUST GIVES A BLANK TONE...NO VOICE/ PLAY BACK AT ALL...i tried various formats and many other call recording apps from Google Play, but no use...all are the same...The playback is not audible..

In the second case of AICP ROM, there is the option for call recording by default in dialler, but upon recording the call, the problem is same as above...It records, but wont play.....

By default, the recorded calls in C drive of mobile are in AMR format...I even tried installing AMR player but the volume is not audible. I transferred the recorded call to other phone and a PC even to check...But in vain..

Please help me resolve it and if its ol, pls send me a reply on my mail id shemrock4u@gmail.com (Mob: 08904628004) .....I need to install the call recording app view professional requirements....

Thanks in advance...

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