Passport Office — surname change in passport

Address:

Jaipur, Rajasthan

my name in passport is first name : manish kumar, surname : blank
i approached PSK jaipur after online application for name bifurcation.
but they refused that "kumar" is not an acceptable surname. it is just a middle name.
all my documents ( matriculation certificate etc) have manish kumar as my name.
any suggestion are welcome.
how to convince them for the same.