A painter and decorator believes he could go out of business after receiving a huge mobile data bill from Orange.
Chris Wilson, from Milford Haven, Pembrokeshire, is said by Orange to have run up the £7,000 data charges downloading films and TV programmes onto his business smartphone.
Wilson has denied the amount of downloads to BB1 One Wales, which is screening a programme on mobile "bill shock" this week.
Wilson told the BBC: "I rung up to pay my bill and the lady said she wanted to warn me that the month's bill was going to be slightly higher than normal."
"Then she told me how much it was going to be - £6,875 - and I nearly had a heart attack. The only thing I did differently to any other month was that I downloaded a TV programme which was 43 minutes long."
Wilson said paying a bill that much could "potentially put his business under".
Clare Harrison, from Haverfordwest, is also featured in the programme after receiving a bill of more than £5,000 for using her business smartphone for downloads.
Orange has accepted that she did not knowingly download the data, and said there may have been a problem with the settings on her phone - but she still had to pay £500 of the charges.
Orange has agreed to reduce Wilson's bill by £2,500, but that still leaves him having to pay Orange more than £4,000.
Orange told the BBC: "Mr Wilson's bill resulted from very heavy and sustained data usage throughout the month, such as streaming films, TV programmes and podcasts on his business account.
"We have sent him an itemised bill with the exact dates, times and the amount of data used. We have acted responsibly and reasonably in investigating this case and offered Mr Wilson a significant and substantial reduction, which he has refused."
Earlier this year regulator Ofcom said it may act to force mobile operators to limit how much their customers could spend on their mobile accounts, in attempt to reduce a spike in other "bill shock" cases as smartphone use has rapidly jumped.