Strange homepage message

Hello,

I sent a test message from my contact form (it wasn’t even a new one), and since then what I get to my homepage is the following:

{“mailSent”:true,”into”:”#wpcf7-f3023-o1″,”captcha”:null,”message”:”Thank you for your message. It has been sent.”}

Why does this happen? Please, could you help me on this? It seems like a problem of the plugin. I tried deactivating it, but nothing changes. Thanks in advance.