Cannot book prepaid M plan (NOT SOLVED)

 My question has not been solved, the answer that Sandro provided only links me back to the same question from someone else which is also unanswered. 

PROBLEM:

I tried to change my package from Prepaid L to Prepaid M. After cancelling my prepaid L i am not able to order a new contract via the website.  

I keep getting this error message

“Ihr Auftrag konnte nicht durchgeführt werden. Bitte versuchen Sie es später erneut oder wenden Sie sich an unsere Prepaid Kundenbetreuung.”

. Help please, i have no plan now and i cannot call customer service as i do not speak german.