Why am I paying for full month when joining a family in the beginning of my cycle?

mishamsk

    I've switched from pre-paid to post-paid T-Mobile ONE plan July 19th and then joined a family plan on August 22nd. However, I've been billed in full twice!.

     

    First statement says: Bill period Jul 19, 2018 - Jul 19, 2018 (weird?), and lists Jul 20 - Aug 19 in Detailed charges section

    Second statement: Bill period Jul 20, 2018 - Aug 19, 2018, and lists Aug 20 - Sep 19 in Detailed charges section

     

    What does it mean and why did I pay the second time in full?

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