Suspect my GF lied to me about something involving money. Placing the evidence here, opinions are appreciated.

6/17 9:36pm

Her- forgot to pay my phone bill. (she lives an hour from me)
Me- It's just a late fee though, if you miss a payment?
Her- I'm ritually a month behind.

She has 2 phones and an Ipad, asked for $275

I sent her the money.

7/2

(asking about her day)
Her- ...My phone got turned off halfway through the day

By my thinking, even if she was a month behind, if she made a payment on 6/17 she shouldn't have service interruption until at least 7/17.

Me yesterday- 9:30 pm the 17th you asked for 275 for a phone bill, then 3 weeks later you tell me your phone was cut off. How is that possible?
Her - my phone bill is always a month behind. So having paid what's past due I still had to pay the current month.

I didn't press the matter but her explanation offered no new information.

I know the knee jerk reaction is that she lied. I'm hoping someone will have some insight on how it's possible to pay a phone bill on 6/17 and have service interrupted on 7/2 even if she stays a month behind.

No "women suck" responses, just some cold hard logic or knowledge of phone billing please.

Any ideas?

Thanks