airtime just gone not sure for what

this is the second month i am having the same problem with cellc, my airtime is used for internet i am not even sure what sites i am visiting called last week thursday was told to speak to the technical department, guy told me to call back friday for a report, guess what called back on friday was told to call back today i am so tired of cellc can i cancel this contract or can i return your handset & you give me a different one because i am have endless problems with this Z3 i am fedup with your service fedup