Sim card bought in 30th of the month, invoiced with one full month amount

Hi, 

I've bought my first sim card in Deutschland, last Saturday, from Media Markt, a pay as you go sim. It was 29th of November. Two or three days later, I've received the 1st invoice for period 29-30 November, in amount of a full month, actually with some extra charge, as the standard rate. It's that normal here, to be charged a full month wenn you just bought and use the sim for only 2 day of that month?

Thanks for answers.