postpaid conversion from prepaid

Hello,

I am trying to contact any English speaking customer executive, any time I call they disconnect the phone if I ask to speak English, I don’t find any email id also for direct communication, this has become too difficult for me now, even in stores you need to go with negative report, person doesn’t even answer your query without it,

Infact I trusted o2 and converted my prepaid number to postpaid, I had a question regarding my balance in prepaid number how can I claim that balance I had 7-8 eur balance in my prepaid number now same number is converted to postpaid 

please help!!

EDIT: verschoben in Englisch  o2_Maria