I'm sure they will cancel it. What types of jobs and which cities did you post?
Review the contract you signed with Career Builder. If it indicated that there were cancellation fees you agreed to them when you signed the contract. If you are looking for a refund of prepaid they won't do it. If you are looking for a way out of a contract you already signed in which you agreed to pay a set amount you are probably bound by the contract. You might try and see if anyone who uses Career Builder would buy your contract if it's transferable or sell the use of your postings and resume search to another recruiter. I don't think any of the boards guarantee results as part of the contract. You could check with an attorney to have them review the contract to see if there is a way out but normally when you sign one you are committed\