Request for Tax invoice

I have registered with Unisa for 2nd Semester 2019. So at work, they required a tax invoice from Unisa since they(Work) are the ones paying for my tuition fees and cannot pay unless I have the invoice. I tried calling with no luck, it's either it rings only or you get to listen to music while you wait, and never get assistance. When I went to Vereeniging Campus they couldn't help either as they were offline. Now I got an Email from Unisa that says if I don't pay I will be suspended. I am really frustrated. Please help me!