Worst account to deal with EVER

This practice's accounting department needs to be improved somehow. I received an account for the first time 3 months after date of admission. Since then I have made partial payments as per my arrangement with them. I skipped a month due to the fact that they "couldn't pick up my payment because I was using the wrong reference" - which was not the truth because I used what was on the statement. They then hand me over without informing me, and after back and forth emails they refuse to withdraw the handover - even now with my account being paid off I'm still being pestered by these debt collectors. Would avoid this medical practice by all means if you don't have full cash payment upfront.