Chandigar c form required

Dear All

we require your Help

we have not shown some CST purchases in VAT returns in Chandigarh . But vendor is asking for either differential tax or C form kindly advise me.

There is a concept called Back lock C form to be issued it is available in Tamil nadu .Andhra,Karnataka also. 

Whether is it available in Chandigar or not.?

Please it is very urgent.