Virgin Mobile internet access

On 6/3, my wife topped up her mobile (PAYG) with £15.
On 8/3 day her credit was almost 0. Checking her account online, her only spendings were 4 texts messages, a couple of calls to me, and 50p for internet access, totalling less than £2
I called Virgin Mobile CS, and the agent said on his screen he could see a lot of charges for using the internet. I asked how come if she paid 50p for up to 25MB of internet usage. He responded 50p is for internet access and then there is a price for every MB.
Long story short, after like 10 minutes of discussion, in the end he refunded a bit over £10 to her account.

To me it makes no sense at all: "it's 50p for internet access and then we charge you for internet access."
And there's no way she could have gone over 25MB limit, at most she uses the internet on her phone to check for the next bus on the TFL site.

Does anybody know what's the internet access policy at Virgin Mobile for pay as you go customers? On their T&C it says "25MB per day for 50p a day"

Most phones have a data usage counter, have you checked this.

50p for first 25MB and then per MB changes after that sounds the most likely scenario.