higher bill than what's mentioned in contract

Hello to all, 

I hope you are doing well.

Last month i bought a phone with contract and paid the first bill of 185.99 € and had to pay 83.49€ per month for the remaining of the contract duration. Which says that i have to pay 60 for the phone and remaining 23.49 for my 40 GB Internet data. But now after the first month i received a bill of 121.80€, 60 for the phone and 61.80 for the data package, even though i have not fully used my 40 GB data and i haven't made any calls. Therefore i would really appreciate if you could help me. 

Regards 

Sabawoon