Unable to dial certain toll free numbers from India iPhone

Many toll free 1860*** numbers from India are treated as ISD calls in iPhone and get "number does not exist" message in American accent. The same numbers work perfectly when dialled from any android phone or land phone.

Is this a bug? Have complained to Apple customer care many times and they have not been able to solve the problem. Ironically, the old Apple care number starting with 1860** was not going through in India!