My DSL contract

In March I purchased a DSL contract at the o2 store in Fellbach. I got the M Flex product which the guy at the store (the seller) told me it was 19,29 on the first 6 Months. And I could cancel whenever I wanted. After the first 6 Months the monthly tarif would increase to 29 euros. 

However on the first Month o2 charged me 38,98 euros. I went back to the store to talk to them and he told me it was wrong, that I would have to call o2 and solve it with them. I called and they said they would solve it. On the second Month, however, the bill came around 59 euros. I never received any bill with the price I agreed on the contract of 19,29. 

I called o2 again, they told me it was wrong because my contract doesn’t cost 19,29. I went back to the o2 store in Fellbach and the guy told me that yes my contract costs 19,20. So he called o2 and told them that they wer charging me wrong, that my contract was 19,29 on the first 6 months. He opened a tread in o2 where it is recorded the mistake. The ticket number is 21443850

He told me that now everything was solved and that I should receive a bill with the correct amount of price of these last 2 months. However, today I received a bill of 91 euros. 

First of all, I only didn’t pay for the last Months because o2 were not sending me the correct price. They are charging me double and triple the price since the beggining. Second of all, It has been 2 months that I’m fighting this, I’m practically begging so I can pay what I owe, but you don’t send me a bill with the correct price. 

I went to the o2 store with my parents and with a friend, they all heard the seller saying that my contract costs 19,29 a month. So now I had to talk to a lawyer, because I don’t know what is happening here. I want to pay for the contract I got. Could you, please, solve this for me now? and send me the right bill? The month of March I paid 19,29. so I owe you 2 Months.