Then probably your WiFi was disconnected for a short time. Turning off mobile Internet should help, yes.

By the way, you posted in the wrong part of the forum. You should have posted in Prepaid.

Hello @yoisa2021,

if you have deactivated your mobile internet on your Smartphone, you should no longer receive this SMS in the future.

Perhaps your router restarted during the night. And even if you don’t use the smartphone, data can be used.

Best regards

Steffen

bs0 Sorry for my late reply even you replied and helped me really quickly! (I saw the comment and said thanks in my heart, totally forgot to do it in a real life...)    
I turned off the mobile internet and it seems like it’s working fine. Thanks a lot for your advice! :)  

o2_Steffen 
I turned off the mobile internet and it solved my problem. I can somehow get SMS still, too. 

Thanks for your reply. I will be careful next time with this issue.

I cannot get the 99 cents back, even I can prove that I really didn't use it on purpose? 

Hi @yoisa2021 ,
it makes no difference whether you used data connections intentionally or unintentionally. Apps often use data connections automatically if network is available. This happens regardless of whether an internet option is booked. But I am curious: How can you prove that you did not use the data connections intentionally? Or did I misunderstand you?
Kind regards
Larissa

Hi Larissa,

I saw the link above and thought it is possible for O2 staff to be able to see my data. My usage of the data happened a little after the time I mentioned (12:05am was the time I received a message, saying the previous date plan was ended) and thought O2 can see what I mean by it. My used data on that day must be very little on the record, too and thought O2 staff can see that on their end and see what I mean... 

Dear Larissa,

I thought about this and I no longer need help nor reply on this. 
Thanks!

Hi @yoisa2021, 

good that you have clarified your issiúe already. 

If you like to avoid the charge of 99 Cent for mobile internet per day, please make sure that you have enough credit on your card at the end of your package-duration. You always get a text-message (SMS) that tells you the duration of the package. If you have enough credit on your card, the package will be prolonged automatically for further 28 days. 

I hope the tipp is helpful for you. 

Loving greetings,

Tobias

Hi Tobias, thanks for writing me a message.

I decided not to talk about this issue anymore.  

But thanks anyway! :) 

Hi @yoisa2021, 

You are welcome.  

We are looking forward to read from you again. 

Loving greetings,

Tobias