Well it's hard to say without knowing what number you are talking about (and if you want you can Email me via my profile and I can try to help)
A couple of tips
It should always be a 10 digit one like 020 1234567 (landline) or if it's a mobile then it begins with 06 and also is 10 digits e.g. 06 12345678.
The of course if this is changed to one with the international access codes then +31 20 1234567 or +31 6 12345678
You can also check in the telephone guide to see if it is listed or not http://en.detelefoongids.nl/?locale=en_NL&newSession=true and of course use google to see if there's any info. Put it with the word "scam" and you might learn more (this is my suspicion from reading your question!)
Otherwise like I said, send me an Email and I will try to help
There are exceptions of course with special lines like company lines, info lines etc e.g. 0900 1234
Of cour