Blink Fitness review: Charged for a full month when I signed up on the 31st of the month.

I signed up at the Blink Fitness in Union, 2700 Route 22 Union NJ 07083, The date was December 31, 2020. I was charged my 21.33 for the month. Then I was charged on January 2, 2021 for the month of January. I asked at the front desk why I was charged the full amount for the whole month of December. They said I was prorated. Then I said if I was told that then I would of just waited until Jan 1 to sign up, then I wouldn't got charged for December the whole amount. They told me to contact customer service number. I have been calling for days and leaving messages and no one calls me back. I would like my 21.33 for December credit back to me.
Thank you,
Melissa Markopoulos