I bought 6gb on the lebara app and I was supposed ...

I bought 6gb on the lebara app and I was supposed to get 2gb free. I have used only 2gb and stopped working, saying that I used all the data when in the app shows that I still have 5bg, but I cannot use it. I try to find a customer service number and I can't find anyone to help me with this. Very frustrating and I don't know what to do.