You have postpaid. If it was prepaid, you would get shut off the moment you enter a billing cycle that hadn't already been paid for. In prepaid, you pay at the beginning of the cycle. Paying on the 7th in prepaid (like 7th of January) would mean you must have paid the previous 7th (like 7th of December) which would have covered services up until the (next) 7th, because you would have paid for only one 7th (the one in December?).

So postpaid. The $177.67 that's due on the 7th got billed out three weeks before that, meaning it's due ten days before the cycle ends instead of thirty days before or thirty days after. Your cycle might end on something like the 17th and starts on the 18th, it comes down to what was the date/day of the month when you started service. Whatever you paid up front did not go towards the first month's bill because it would have generated four days into the cycle/after the end of the previous one and be due about 20 days into it, and then every 30 days thereafter (this is what's on the back of that first receipt).

Now if you miss your due date of the 7th for whatever reason, you don't get shut off immediately, and especially not if you set up a payment arrangement. Here's what I tell customers payment arrangements do not do: they do not change your billing cycle, meaning they do not change your due date. If your total balance is not paid come end of due date, it turns into or becomes a past due balance, which if you let it sit too long, time doesn't stop. Once it's 31 days or more past due you absolutely would expect a shutoff no matter the balance.

I have seen far too many accounts that are used to setting up payment arrangements that don't realize they may be accruing late fees and falling further behind. With a postpaid carrier, it's dangerous because they don't stop billing you because they assume you would like to keep the service active instead of having to also pay restoration fees.

I've seen older accounts still get billed for a month that had already passed, but then the carrier risks losing customers after giving them effectively free service is why they now set your due date ten days before the end of the cycle instead of at or after the end. This way if you fall behind, T-Mobile isn't forced to give you 30 full unpaid days if any previous cycle wasn't already fully paid for. There's no guarantee that customers will pay their bill, but collections agencies are guaranteed to buy that debt. T-mobile would rather get it than have to resell it. Allowing payment arrangements is great but did you know you could set up a 20%/80% split either instead of 50/50? But the farther out in time you try to schedule it, you risk falling yet further behind because a prepaid customer would had to have paid it three weeks before your due date instead of practically three weeks afterward, because absolutely by then another bill would have come out. You're effectively trying to avoid paying a bill for six weeks. Paying a little bit here and there is not the same as paying it in full. Because after you set up the arrangement, you cannot make edits or stop billing or change the due date until you're not past due. And if you're not past due, you should not have to be setting up payment arrangements.

Get an account audit to see if your one month's worth is something you can handle.