how to calculate interest 234 b , 234c in case of relief u/s 89.

i hv received intimation of cpc charging interest 234b,c . i hv received arrears of salary. my tax was deducted in tds. no tax was due to me. ihv claimed refund in return , despite of it i received demand on acc of interest 234b,c. i want to know. tax liability due is calculated before relief 89 income or after deducting relief. please share.