0991 is not a country code. Numbers inside a country start like this: Deggendorf (Germany), Urumchi, Xinjiang (China), Airtel (Congo - Kinshasa), IR-MCI (Iran) 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 |
|---|---|---|
 Deggendorf · Germany | +49 991 … | 0991 … |
 Urumchi, Xinjiang · China | +86 991 … | 0991 … |
| Urumqi, Xinjiang · China | +86 991 … | 0991 … |
 Airtel · Congo - Kinshasa | +243 991 … | 0991 … |
 IR-MCI · Iran | +98 991 … | 0991 … |
 Airtel · Malawi | +265 991 … | 0991 … |
 Claro · Paraguay | +595 991 … | 0991 … |
 Claro · Peru | +51 991 … | 0991 … |
 Dito · Philippines | +63 991 … | 0991 … |
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.