Unexpected response

I have an Asus Max Pro M1.
Recently I have discovered the phone does not work properly .
My family kept asking me why I dropped my calls too early that they could not answer. Later, I realised that when phone of the called party was ringing, my phone returned with a "engaged" sound and I dropped the call.
I have done several experiments on the issues. Some conclusions drawn are as follows:
1. The problem happens constantly on some telephone numbers of called parties, no matter which SIM slot my SIM is using;
2. When my SIM is used in other handsets, it works perfectly.
1
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Comments
Did u checked with ur service provider on this... Also check for any system updates to fix this issue...
Hi winkienampapa,
We have improved this behavior in the latest Android 9 update: WW- 16.2017.2007.084.
Please check update in Settings->System->System update.
Or manually update from our website: https://www.asus.com/Phone/ZenFone-Max-Pro-M1/HelpDesk_BIOS/
The firmware file will become available in a few days. Sorry for the inconvenience.
How to update firmware on my phone? | Official Support | ASUS Global
AJ1, I had checked it with the service provider.
The misbehaviour has disappeared recently.
The system is 16.2017.2007.084 dated 20200706.
It happens to airtel to airtel calling, it's their normal ringing tone. I was confused at the beginning too.
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