Hello Kashyap Deepak,
It's normal for the oscillator frequency to decrease or increase as capacitance changes. The way you calculate it is FREQ = 1/R x C. If you are still using the LM555 then there are other factors which will affect your oscillator. The LM555 switches at 1/3 and 2/3 VCC. These limits will affect your reading.
The CD4060 doesn't have all of these problems. It is much simpler to deal with.
You seem to be hanging onto the LM555 because of a printer circuit board previously laid our. What's wrong with doing another PCB? I would estimate it wouldn't take more than 30 minutes to layout one. If you need help just redo the schematic and I will lay out a printed circuit board for you. You can do a board your self. It really is easy.
Regards,
Charles Bannister