Cancelled, but still being invoiced

I cancelled my account with them on the 27th of January 2021. I even received a phone call during February confirming that I am in my notice month. Low and behold I am still being invoiced two months later.

When I try to contact their call center, I am caller number 20. I am not going to hold for half an hour to speak to someone. I have emailed them for credit notes on the invoices for March and April. I will update this when I get a response.