Student broadband cost changed

Hi, I signed up to the M250 Fibre Broadband deal for my student house. The first payment has gone out fine but I can see the price of the second month is much higher when I was expecting it to be the same every month.

I rang up earlier in the month and was passed between different agents and the last person I spoke to (for 45mins!!) said she'd fixed it, but wouldn't make a note of it on my account or send an email to confirm that. I'm worried that she didn't sort it and my next payment will be much higher.