First of all, I am writing this post because the BDO agents doesn't help. They don't even know what numbers to enter. I just wasted my time when I decided to call them and ask...
MERALCO recently changed some subscriber numbers as part of their upgrade of computers in certain branches I think. So I had to re-enroll my account.
So here's the procedure:
1. Go to "Pay Bills" icon.
2. Click "Enroll Company/Biller".
3. Choose MERALCO from the drop down menu. Subscriber Number is the FIRST 11 DIGITS of your ATM/Phone Reference No. (You can see this at the bottom part of your bill) Subscriber Name is the name registered in your bill, you can find this at the top of your bill. Enter your preferred nickname then click Submit.
4. Click the "Pay Bills" icon again when you receive the confirmation of enrollment.
5. Choose which account to pay from then enter MERALCO in the biller section. Doing this will show your Subscriber No. and Name. It will ask you to enter an ATM/Phone Ref. No. Enter the LAST 5 DIGITS of your ATM/Phone Ref. No. (this changes every bill)
6. Enter the amount then click Submit.
Pay your bill on time bcoz BDO Online doesn't accept overdue payments. I guess the last digits of your ATM/Ref. No. expires. Good luck! :)
**UPDATE** October 21, 2015
So if all else fails and you cannot pay your bills online, try going to the nearest SM Bills Payment. I heard they can now accept late payments until 6 or 7 days past the due date. Cool right? Thank you, SM! :)