Phone Respond with text - SMS send error

I noticed about a week back, when I respond to a phone call with text (when I am not available to take call), the SMS is sent to incorrect country code (+60). The correct correct country code is +65. The caller contact is also +65 in my contact list.

I am currently using iPhone X / iOS 15.3.1. I moved the SIM card to an older iPhone 6s. This issue is not present with iPhone 6s.

Country / Region is set to Singapore (+65)

Please advise how to fix this.

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