Please tell us some basic information before asking for help:
Model Name: ASUS_X01BDA
Firmware Version:
Rooted or not: NOT ROOTED
Frequency of Occurrence: VERY FREQUENT
APP Name & APP Version (If your issue relates to the app): PHONE/ CALL
In addition to information above, please also provide as much details as you can, e.g., using scenario, what troubleshooting you've already done, screenshot, etc.
I've noticed this call waiting problem around 9 months ago tried many ways to sort this out sadly I couldn't.
I have turned on the call waiting settings in Phone(Dial Pad)>> Settings>> Calling accounts>>Sim1 (eg XYZ)>>Additional settings
Looking for help for this issue.