Each credit bureau has their own way of computing a credit score. The algorithm of how the credit score is calculated will differ and thus the credit score that all three bureaus calculate will not be the same. Banks report your credit activities to the credit bureaus who have different mechanism to arrive at the credit score. Though the parameters to calculate the score are the same, the weightage to each parameter is different. Thus you see a change in the credit score with each credit bureau.
There are four major credit bureaus in India that compile your credit borrowing habits and use that information to fabricate a credit report: CIBIL™, Experian, Equifax and Highmark. These bureaus have their own way of getting their credit score and reports done. So you cannot expect all the credit bureaus to come up with the same credit score. It is possible that your credit score might be lower in Equifax because their calculation may vary from others and thus this might have made your score go down. Or there is also a possibility that there might be errors in your credit report and therefore this affected your credit score. If that is the case, it is always better to get your credit report checked to avoid such problems.
Do you want to check the status of Equifax credit score? You can check here for free.