Amazon — amazon prime

Good morning, in november, 2017, i ordered
Amazon prime. I signed up for the free 30-day period. After ordering a few items for christmas, i found out my husband, stephen, already has amazon prime. I therefore, cancelled my amazon prime before the 3o-day free trial period. I then saw a charge of $11.94 on my credit card statement. I was hopeing this was a mistake and would be credited on my february 2018 statement. I have not been credited and i should not have been charged for the free 30 - day trial. I cannot locate any number on any amazon websites to call for customer service, therefore, i need your help! Thank you, catherine hubbard