Sprint Employee signed as Lessee on my cell phone contract/lease agreement?

Hello! I just signed up for service with Sprint two months ago. The salesperson told me I qualified for two iPhones and that Sprint would be paying for those phones as part of a new customer promotion. Upon receiving my bill for July I noticed I am being charged for leasing the two phones. I looked back through my emails from Sprint and noticed that the salesperson signed every line on every document, including my "lease agreement" under "lessee" or "buyer." I never saw or signed any documents when I acquired Sprint's cell service or phones, they were emailed to me after the fact, signed by the salesperson. I am wondering if the Installment Agreement/Lease Agreements are valid without my signature (I am the only one on the account) and, if not, what my course of action should be. Thank you so much! Jana Manke