I got tricked into O2 contract.

Hallo O2,

For past 5 years I want to get out of O2 telephone service. This year fortunately I got my cacellation on October2018. But yeasturday I got call from (+4917688854760) this number asking me if I want another contract or not. I told her that I am looking for prepaid contract not post paid.

And then she started telling all other contract schemes. During the discussion with her I liked one contract. And minute I said I like, she started speaking for 2-3 minute (all in german... which I had no clue) and at the end she just said you will receive everything by email you can look into it. and without hearing anything from side she just said chuss and BANG! hang up my phone.
My German is not that good, I did not understand what she is talking about, I was under impression that she is talking about prepaid connetion.

Even in evening I tried to call her, first just hearing my name she cancelled my call, in second call she picked and I told her that I don't want postpaid (realizing that morning talk may be for postpaid), again she said something and again allowing me to finish what I say, immediatly she cancel my phone again saying chuss.

And today morning I got Email stating I got new contract, I have to 14 Euros of O2 extra plus and 6€ mothly for next 24 months.

Why?
You can not cancel our contract on phone but you can give one on just phone? Without reading or understanding it ?

And after I want to talk to these people they just give each others numbers. I called (017688855222) they said call the same telephone number from which you received contract. When I call on (+4917688854760) they said call on (017688855222).

And I am stuck with this contract for rest of my 24 months. Can anybody help me what should I do? I don't want this contract.