Payed price for old tariff despite changing to new tariff online

[CatTrek]

I recently changed my tariff on o2 to the 18month 5gb sim only unlimited mins and texts tariff @ £12 p/m yet my latest bill came out as the price for my previous tariff @ £13.32 which was a 2gb 12month unlimited mins and texts plan. Looks like the next bill is going to be the same price again?
My o2 app says my tariff is the correct one with the correct price but the bill is still the old price?
No online help or store help due to virus so anyone able to help on here? Many thanks

[jonsie]

What tariff is showing in My O2?

[CatTrek]

The tariff showing in My o2 is the tariff and price I switched to 5gb unlimited mins & texts £12.32 (. 32 being the standard extra tariff rises) while my bill is still the price I payed for my last tariff 2gb unl m&t @£13.32 I don't have any idea why its not charging me correctly as it went through fine and shows correct data and such but I'm getting billed the old price.

[MI5 · Accepted solution]

@CatTrek 

The first bill after a tariff change is an amalgamation of your old and new.

I would expect it to be correct after a full month on the tariff.

[CatTrek]

Got the confirmation email for the change on the 10th March... Will wait for next bill on 7th April and see if the goes to the correct price. If not I will come back here for further help.
Hopefully it corrects by next bill I will check back once that comes through.
Many thanks
CatTrek
Stay Safe!

[MI5]

You too

[CatTrek]

New bill came through and it has switched over to the new price.

[jonsie]

Excellent @CatTrek