iPhone 16 Pro Max cellular data not working

Recently purchased a new iPhone 16 Pro Max (iOS 18.1) from Apple The Exchange TRX, Malaysia. I am currently using the device in Maldives. The mobile number I am using is from Dhiraagu network. All calls and sms works without any issues. But data is not working. I have tried a mobile number from Ooredoo and it works without any issues. Dhiraagu carrier still not able to find the cause. I have not used the phone in Malaysia network. The data only works for a while after the phone is switched ON or after I switch ON/OFF Airplane mode. I have done following, but still does not resolve the issue:

• Reset Network Settings
• Factory Reset
• Erase All Content and Settings
• Tried with eSIM and physical SIM
• Airplane mode ON/OFF several times
• I have installed the same eSIM and physical SIM to the another brand new iPhone 16 Pro MAX, but still does not work.

Anyone else had this issue? Any ideas to resolve the issue? Could it be due to iOS 18?

Thanx for any assistance.

[Re-Titled by Moderator]