Misleading advice and information from consultants

I took a contract cellphone which was activated last week Wednesday. I wished to terminate the contract early due to valid reasons. I called the customer line enquiring about the process as well as the terms and conditions and was advised that I can return the phone, without any charges as long as it's still within the 7 days cooling off period. When I went to the store, was given different information. I was informed that I can't return the phone if it's been opened,there's nothing that can be done. Nothing was mentioned about the cooling off period.