0831 is not a country code. Numbers inside a country start like this: Kempten Allgäu (Germany), Yibin, Sichuan (China), Belgaum, Karnataka (India), Habiganj (Bangladesh) and others. The first digit 0 is the trunk prefix for domestic calls and is dropped from abroad.
Have the full number? Check it in the number lookup.
| Area or operator | From abroad | Inside the country |
|---|---|---|
 Kempten Allgäu · Germany | +49 831 … | 0831 … |
 Yibin, Sichuan · China | +86 831 … | 0831 … |
 Belgaum, Karnataka · India | +91 831 … | 0831 … |
 Habiganj · Bangladesh | +880 831 … | 0831 … |
 Vodacom · Congo - Kinshasa | +243 831 … | 0831 … |
 AXIS · Indonesia | +62 831 … | 0831 … |
If a number starts with +, the first 1–3 digits are the country code. If it starts with 0 (8 in Russia and Kazakhstan), it is a domestic number: an area or operator code follows, and from abroad the 0 or 8 is replaced with + and the country code. The same digits can mean different places, so where the call came from matters.