0521 is not a country code. Numbers inside a country start like this: Bielefeld (Germany), Steenwijk (Netherlands), Rangpur (Bangladesh), Vänersborg (Sweden). The first digit 0 is the trunk prefix for domestic calls and is dropped from abroad.
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| Area or operator | From abroad | Inside the country |
|---|---|---|
 Bielefeld · Germany | +49 521 … | 0521 … |
 Steenwijk · Netherlands | +31 521 … | 0521 … |
 Rangpur · Bangladesh | +880 521 … | 0521 … |
 Vänersborg · Sweden | +46 521 … | 0521 … |
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.