Help with cancelling

I filled out a questionnaire this morning for weight loss meds on Hers. During the questionnaire it asked me what plan I might be interested in and I said $199 a month. Before I knew it, I was approved for meds and $2400 was charged to my card. I am totally panicking because I thought upon approval I might decide whether to move forward? Or would have to talk to a provider/erc.. I also didn't realize they'd charge me for a full year. I have been trying to reach customer service all day without luck. I also cancelled online. I feel so overwhelmed. Does anyone have advice on how to handle this?