mobile

hallo , i have O2 booster package i pay every month 39 euros ! since 2 weeks i have been shifted to prohlis dresden and my mobile data is not working ! before my speed was about 300mbs per second now it is 0.65mbs per second ! i went to the O2 store where i had this contract and they said we can't help you ! you should send the screenshots per post ! i don't understand what should i do and he said i can't even cancel my contract till 2027 ! if my data doesn't work why should i have to pay till 2027 . plz help me regarding this