(Yearly contract) After 2 months monthly payment rise?

[KaylaFG]

Hi everyone,
I ordered the Yearly contract, Bill started at £6 pm in Feb. (including VAT)

From April and this month, May, my bill rises to £6.70.

Read through my bill details, I only have a Tariff charge.
Does anyone know why? I try to find the answer on my account.

Thanks 

[Cleoriff · Accepted solution]

@KaylaFG 

Yes it's the annual Retail Price Index (RPI)

https://www.o2.co.uk/prices 

[KaylaFG]

I found my answer. Thanks.

But don't know how to delete this post.