Hy @Dydycom thanks for your request regarding booking the option o2 my prepaid l. 
The price of 9,99€ was for the first 4 weeks. After that time, this offer is charged with reguarly 19,99€. 

That should be the reason why you received the answer, that there is not enough money on the account. 
kindly regards
Michael

Thank you for the info. 

@Dydycom you´re welcome. If there is anything we can do for you feel free and write us. 

best regards
Michael