No invoice nor statement and handed over to debt agency

The lancet accounts department is useless. I got an sms that I was being handed over to debt collectors. I had not received an invoice/statement for over a year. I had to call to get an invoice, On their online management system it showed they had not contacted me in over a year. Now their debt collectors wont acknowledge my proof of payment. They just ignore my emails. The whole thing could have been avoided if they had just sent me an invoice or even mentioned it when I went for my monthly bloods. These monthly blood tests are always pleasant, the branches I visit are great, the phlebotomist are great. The accounts department makes me want to switch to Ampath and have left a very bad taste in my mouth. Thus the 1 star.