vat input refund in case of excess sales of cst

sir , i am a computer dealer in karnataka, now i have some query regards vat and cst , pls try to help me regarding this

suppose i purchase goods from local vendor under 5% and send the goods to west bengal at 2 % cst, then the tax difference of 3 % is supposed to be refunded by the government  or not

weather cst sales can be set off with vat input credit and even after clubbing the vat output and cst sales my vat input is more due to major cst sales compare to local sales then what to do

example

vat input is 200000

cst sales against c form is  80000

vat out put is 20000

then my vat laibility/ refund will be 200000-80000-20000=100000

if this is right then how will i get the refund and what time