Can we put this to bed now, it's clear what the answer is. While VM employees should know the answer to simple questions, they have a track record of giving incorrect information.
The roam like home policy states -
"You can now use your UK allowance anywhere in the EU with Roam Like Home. This means that while you’re travelling in an EU country you can use your UK allowance of Minutes, Texts and Data, just as you would in the UK subject to fair use limits."
You are billed monthly and you use your data monthly, not daily. The legal terms and conditions for the oomph bundle have been linked to in this thread which states that while roaming, you have to abide by the roam like home policy.
Also in other documentation it states a monthly data cap, not daily.
"5. Under Roam Like Home Regulations we may apply a monthly data cap. If you use more data than the monthly cap allows we may apply a surcharge to any data above the cap. The data cap and surcharge is set by the Regulations and depends on the price of your airtime plan.
5.1. It’s a simple calculation:
5.1.1. Pay monthly customers: twice your monthly airtime cost (before VAT) divided by the current EU data wholesale capped rate.
5.2. You can see the surcharge rates and the latest EU data wholesale capped rate in our Tariff Table. Alternatively, why not use our calulator, which can be found here."
Just to make this 100% clear, that roam like home is not daily, if you take the £23 a month sim card with 40GB of data and input that into the roam like home calculator, it allows you to use 9.88GB of data while roaming. If that was daily, it would give you a total of 306.28GB to use in the month of August. How is that possible when you only have 40GB a month.