For peace of mind, this might help you too. I figured this out thru their Frequently Asked Questions since I was confused with my first billing. I emailed them and they won't answer queries clearly and will only give SOAs or automatic responses.
NOTE: Understand that your initial payment consists of Security Deposit (SD) + Installment Fee (IF). It's NOT an advance payment/ for a recurring mainline bill, it's the INITIAL Subscription fee. Your security deposit is refundable once you terminate the subscription (which Idk how).
In my case, I ρáíd the whole upfront free: (SD) P1500 + (IF) P2500 = P4000 total subscription fee. I have a P1500 that I can refund.
My net was installed on May, 2. Statement of Account (SOA) will be read every 1st day of next month which contains your billing. Do not pay unless you receive your SOA. I received my SOA thru email on June 9 and my first bill amounts P2951.62. I received an SMS before that day that my outstanding balance is P1451.62 (it will be confusing when you don't know the computation, see computation below). I was so confused and distrusting because I didn't understand my first billing plus I ρáíd P1500 on June 2 without SOA, it wasn't reflected on the billing. So I emailed, yet my questions aren't clarified. This was during ECQ, so it's frustrating to contact them.
Here's what I understood;
The first Mainline fee is computed from the Day of Installation to the End of its Month. It's also known as Prorated Charge that you're ought to pay + Mainline fee of the Recurring Month.
COMPUTATION: Mainline Plan / 31 (Installed Days) = Prorated Charge
+ Recurring bill + Payment for IF when stagerred
= Total amount of the first bill (VAT Included)
My first bill compute: P1500 / 31 * 30 Days = P1451.62
+ P1500 (June bill) + 0 (IF)
= P2951
The next SOA will consist only of your recurring fee once you ρáíd your first bill. Due date of payment varies but mine is every 20th day of the month, which is unfair for me but safe for them. Just email them if you have more questions, maybe they would reply.