Why am I getting bill after contract termination

Dear O2

Now why am I getting bill again When my last bill which 27th in September as my contract which terminated on Aug. 2015?

See info below as

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Invoice date:  01/10/2015

Invoice number:  189********1/04

Your Customer number:  97*******98

Dear K*******,

Thank you from 28.08.2015 - 09.27.2015 have used the O2 Services.

Your current account amounts to: Total amount 2.58 EUR

On the following pages you can find a detailed breakdown of this bill.

Please transfer the open amount of 2.58 EUR until 09.10.2015, stating the

ID 97984298 on our account at UniCredit Bank - HypoVereinsbank (BIC

HYVEDEMMXXX), IBAN: DE16 7002 0270 0005 7131 53. Thank you!

Best regards

Your O2 Team

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I am really disturbed with thesis bill, is this fair to charge like this ?.

Can you please tell me why I have this bill?

Thank you.

Rg

Piyush