Frustrating finance dept.

Been to Lenmed hospital on the 15th may 2020 payment of my account was made via their link they sent through at the end of may as i have informed them till today 15/02/2020 still getting sms's from ER Consulting and Nudebt saying that i owe money that has been paid last year end of may already. What more do you guys want?! They have proof of payment yet they are still investigating since last year and sending messages to say that i havent paid. If the finance person cant do their job find someone else because this is becoming really frustrating and you guys are messing up my credit score for nothing.