Pathcare-trys to double charge by handing paid account to lawyers

Last year on the 29th of November I had tests taken at Pathcare in Kingsbury hospital. I was pregnant at the time. I paid the full amount on the day and luckily for me I had kept all my slips in a file. FFWD 10 months later I get a call that my account has been handed over. I owe Pathcare for the bloods taken in November. No one calls me to enquire about this, my account is just handed over. I've sent through my pop but cannot understand why this was not captured on their system? why I was not informed before... plus, how affect my credit score? it's really not fair that Pathcare doesn't do a good job of checking their system and letting people know before handing them over. os it perhaps not a **** from their side to make clients pay double? what if I hadn't kept my receipt?