0837 is not a country code. Numbers inside a country start like this: Aba, Sichuan (China), Mine, Yamaguchi (Japan), Jhal Magsi (Pakistan). 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 |
|---|---|---|
 Aba, Sichuan · China | +86 837 … | 0837 … |
 Mine, Yamaguchi · Japan | +81 837 … | 0837 … |
| Nagato, Yamaguchi · Japan | +81 837 … | 0837 … |
 Jhal Magsi · Pakistan | +92 837 … | 0837 … |
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.