Landlord threatening arrears over rent I've already paid?

I'm being told that I'm three months overdue on rent. I'm not, I'm completely up to date.

I'm a student, so I have the option of paying my rent monthly or in large installments as my student loan comes through. I choose to pay in installments.

I'd communicated with the landlord about this, they said it was absolutely fine and even gave me exact dates and amounts.

I last paid on September 23rd and I'm due to pay again on Monday. Business as usual as far as I'm concerned. But got an email a few hours ago saying I was 3 months overdue and I have 7 days to cough up the cash.

I've responded with screenshots of the emails previously arranging my payment plan, and my bank statement showing the rent being paid.

Probably won't get a reply till Monday now. Do I have anything to worry about or is this just a mistake?