I've been charged and still can't send a refund request because I don't have a paid account

Hi,

I've been charged a week ago with 159.00 $ without realizing it till now. As I'm not using Prezi and didn't want to upgrade it I was trying to follow the process to get a refund and after that remove my account to avoid future charges and to my surprise I can't send the required "help request" because I don't have a "pay account".

Could I get some help on this? 

Thanks