O2 switch up and monthly bill

[Osa9595]

Hello I have bought my first mobile+sim contract on 29 sept this year. my first bill generated on 1 oct and due date was 15 oct. On 13 oct (16th day ) I have upgrymy phone to another phone using o2 switch offer but kept same number.I checked today my account direct debited for my last phone and airtime plan for full month when i only used it for 15 days. Can anyone explain this?              Second thing, I have used switch offer to upgrade, I believe i dont have to may remaining installements for old phone. i only have to pay for new phone monthly installments and new airtime plan . Am i right??

[madasaf1sh · Accepted solution]

@Osa9595 

That is because when you used switch you direct debit will have been processed and cant be stopped so your first installment and airtime will have been debited, so the bill is correct, and the system will correct itself. 

On your next billing date it will be the new airtime and device plan. 

My advice to avoid this is to change device before your billing date.