Tesco Mobile hooligans

Hi there,
I contacted tesco mobile last week after I discovered that I was charged €245 in data charges for one month!! I’m signed up to the €30 per month tariff with 15GB data. I’ve been with them since May 2017 and to be honest I’d barely use even half this data as I only use it for reading newspaper articles, checking weather or my daughter might put on kidstube. Have never watched Netflix or anything which would consume a lot of data, phones are just not my thing. Normally my bill would itemize when I accessed data e.g 2.33pm, 4.15pm etc but for a whole month huge amounts of data were being used up at 11.59:59 every single day for that month??? WTH?? Then it stopped and went back to normal after the month wa up?? Got a phone whizz to check my phone for maybe apps that I didn’t know were there but he found nothing. The guy in Tesco I spoke with thought it sounded a bit strange alright seeing other months and month after I’d very little usage and he gave me a case number so that it could be investigated. I had to ring back (to care would they ring me!) and gave the guy on the phone my case number. He asked me did I ring that number!!! I said it’s a case number - LOOK IT UP!!! He said you’ve been charged cos you’ve been using more data then you’re allowed. (You don't say...) After 15minutes of trying to explain I didn’t use this data and there was clearly a blip with their system, he said no it’s accurate and then managed to find the “memo” from technical team saying it “appeared” I was in control of my usage so my fault essentially. I have WiFi at home also but they told me that I’d still be using data. I am adamant that no excess data was used as this month was no different to any other. I’m going to contact ComReg but just wondering if anyone else might know what’s going on or has experience of same?? The excess data started on 15th Jan and charges incurred then from the 22nd Jan. Got a text from them on 2nd February to say I’d used 80% of my credit limit. They can’t tell me what this was about....They also told me there is no onus on them to warn customers when they’re reaching their limit....
Thanks if you can advise or help.....