RCS BILLING ERROR, HANDING ME OVER FOR THEIR MISTAKE

Just got an SMS threatening me with collections telling me to make an urgent payment. The invoice in question is dated 12 Jan, I paid it on 11 Jan at Markhams so the payment went through right away. You lot have matched my payment to my open balance rather than to the due invoice cause the invoice only generated as an open invoice on my account by you on 12 Jan. So telling me on the phone today Sorry, we are not going to fix the mistake, that is not going to work. Please do a journal to unmatch my payment from my open balance and match it to the invoice dated 12 Jan. I have emailed proof through and whatsapped too.