I use International Direct Dialing (IDD) to call numbers in India. My cellphone operator Starhub, provides the international call prefix 018 that can be prepended to Indian phone numbers to make the call. These IDD calls are far cheaper than ISD calls. This was working fine on my Xiaomi Redmi Note 4 phone until a recent software update. After that, it started prepending the Singapore country code +65 to the number that already has IDD prepended to it. Thus IDD 018 calls stopped working.
Open the Settings section of the dialer: Phone (📞) → hamburger menu (☰) → Settings (⚙). Go to Location and disable the Add country code option. I think this option was added recently in a software update and it was enabled by default. After turning this off, I was able to make IDD 018 calls without any problems like before.