Delay problem being made my problem

I gave birth in November 2013 and apparently Lancet was not paid by the medical aid which I no longer use. What upsets me is that they did not process the claim again in January when the medical aid had funds or bother telling me I owe them. Only this year in 2015 they start calling & sending text's reminding me to pay them. I called my old medical aid and they said there was no claim. I do not understand their policies or how they are working as it is annoying getting these calls & being threatened with legal action. Should they have let me know in good time or the medical aid i was using at the time they would have been paid, asking for your payment so many years later is not on & the harassment is a no go.