2nd bill higher than expected

[E2023]

I’ve recently joined O2 about 2mths ago now. First bill fine £20 mthly bill as per contract. However 2nd bill is £23- something (17% more than I signed up to). I’m sure the annual increase wasn’t 17%!
I haven’t gone over any limits, and cannot see why I’ve now got a higher mthly bill. 
Tried to contact O2 online for a supervisor, but they’re busy. 

[Enlli · Accepted solution]

RPI plus 3.9% gave a rise this year of 17.3%

Thr annual rise is well published on the website and forms part of the Terms and Conditions to which you agreed