AOK charging me an absurd amount of money and no reason.

I moved to Germany last year start of September I started working the 1st of October and was insured by AOK then I got fired start of January and started working again in a different job start of March till middle of July. I was obviously insured during this time because I would not be able to work otherwise. I quit in July since we were moving and I was starting university the following October.

I’m not too sure what happened to the insurance between middle of July and end of August but when I got my university offer I connected with AOK and then they sent me a letter with student insurance which is €140 a month I filled it out and everything and the following October I paid the € 140.

And now I get a notification from my banking app that there is a pending payment for 17th of November of 1800 and something euros from AOK. I have no clue why would they be charging me so much money there is no reason behind it and i can’t do anything that since it’s Friday I can’t even call them or get any support. I don’t even have that much money so I have no idea what to do, if anyone was in a similar situation or knows what this is even about.. anything would help.