Maybe that limit is to prevent blocking of HDFC DC for suspicious tnx
If bill is above 20k, you can pay in parts also
There's a cooling period after adding a new biller on HDFC Billpay
Security Control Credit Card:-After registration 2 hours no trxn allow, between 2 hours to 24 hours limit of Rs. 10,000 and after 24 hours limit upto 2 lakhs.