Billing Issue

Dear O2 Support,

I am an O2 customer having "O2 Free S plus - 2017" package on number +49176xxxxx033. I have been using it for almost 18 months now.
Yesterday i received my monthly bill amounting 78.08 EUR which is very high because i pay 23.99 EUR for my activated package.
I had received a call last month from O2 customer service regarding free boost option to O2 FREE M BOOST.
Your representative said that i can cancel the option within 14 days if i want, without paying extra money or providing any reason.
I wrote an email to shift my package back to the original one i.e O2 Free S Plus within first 1 days. It was done as per my request
But in the latest invoice, i have been charged 33.604 EUR connection price and 10.00 EUR service charges
Why have they been charged when i was being told that the boost option is free of cost and the cancellation within 14 days would be free of cost as well
It is my humble request to sort the issue and provide me with a feedback.

Regards,
Haris

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