The first thing I do in that situation is I try ringing from 3 different providers, because that's a very quick test - sometimes some providers fail to route while others route correctly.
If they all give the same result then you need to talk to your provider about whether they are routing calls to you.
You can even try on the new system to ring an internal number by dialling its full external number so that it routes out to the provider and loops back to see what happens.
*** If I am setting up a new service, I usually put in my test number to the DiD form in every format I know the provider might present it as - ie, in Australia 8 digits & 10 digits. That way I don't have to worry about whether the DID form is correct until after I am getting successful calls.
