Terminating O2 free M boost contract before 2 years

Hello O2,

i came to Germany two months ago as an exchange student and i will leave again back to my country on 30/6/2020

i was interested in the O2 free M boost sim card contract for 20 euros per month to get 20Gb internet and unlimited calls but the man at the O2 store told me it is a two year contract and i am only staying for about 8 months more

I want to know what will happen if i sign the contract and decide to cancel/terminate it before i leave?

do i have to pay any extra cancellation fees? 

than man told me you can only terminate it after 6 months, does this mean cancellation will be for free after the 6 months?