Never join their health they will bleed you dry when you leave

Before leaving the country, I asked numerous times what I should pay in before closing my account and had additional payments loaded and paid additional month to ensure I'm covered. HOWEVER, months later they reached out with a random amount that I owed after giving 2 months notice and I asked many times to prove where this amount came from and no answer, now they gave me over to debt collector but still I have no clarity on the amount.