I used to work for Vodafone and once had a call from someone who got the ferry over from Dover to Calais (pre-brexit). Apparently he didn't realise his phone was on in his pocket and used like 5mb of data (just through weather/ambient apps or whatever I guess). They charged him about £30 for it. They literally charged £6 per mb. When I spoke to general customer services to see if this was a mistake, they said the charges were totally legitimate and that he wouldn't be refunded for it.

Absolutely ludicrous.