Amazon Prime - Unauthorized Debits

I placed an order with Amazon in May 2018. That transaction went well. There was an option to join Amazon Prime but I declined, as I was not planning to place any orders again. To my surprise, I noticed that there were deductions by Amazon Prime on my credit card every month since then. I am unemployed now and I cannot afford to pay this. The crux of the matter is - I NEVER AGREED to activate Amazon Prime membership or to the deduction. Please assist me with a refund of these deductions.