You mean total due amt in the statement or current total outstanding? BBPS does not support paying more than the total due amt in generated statement anyway.
That is how BBPS system works. If you want to pay current total outstanding then try paying directly via cred or credit card issuing bank's own portal.
Oh I think they have stopped it now. Paid my SBI credit card bill on HDFC app bill payments and didn't get the 1% cashback on easyshop platinum debit card.