Unexpectedly high bill for additional phone - NOT WHAT I SIGNED

[phoneuser]

Hi, I can't get through on the phoneline due to call volumes so maybe someone here can help.  I recently added a second phone to my plan for my son, the package including phone hire, airtime and insurance was £22.  I reviewed this with the customer service agent in the O2 shop the day before lockdown and was happy with the price.

I got my first bill today and the cost for my son's package on my bill is nearly £29.  This is not what I agreed.  I can't figure out the extra charges - he hasn't made any calls and pretty much only uses WhatsApp via WiFi so he's not using extra data.

Can anyone explain why this might be?  I can't figure it out.  I paid half of the phone upfront, to keep monthly costs near to £20, and I know it sounds ridiculous but my budget is pretty tight, so there was a reason for going for this package.  I just missed the 14 day cancellation, so I'm stuck with it, but if anyone can shed any light on the extra costs that would be helpful, as I understandably the phoneline is short staffed and you can't get through to speak to a person to query anything.

[MI5 · Accepted solution]

It should all be explained in your MyO2 http://www.o2.co.uk/myo2

[Bambino]

@phoneuser It may only be a pro rata charge for your first bill on that phone. Check your MyO2 as @MI5 suggested.