sars dispute

Sars has not been communicating, I received an email today serving a final notice to pay R13989.83. I was unaware that I am owing Sars neither do I now why I am owing as I am taxed every month from salary and my company does the e-filing automatically. They are giving me 10 days to pay or make an arrangement. I have been trying to call since 8am up until 4pm. I hold for a long time than my call gets dropped