Phone call When will you pay

I just received a phone call from Cell C asking me when will I pay my account as the due date was yesterday the 21st (a Sunday) and I have not yet paid (Today is the 22nd) I have never been so insulted in my life that a company phones and asks when will you pay the following day. Is Cell C experiencing financial problems that they need to phone clients and ask them questions of this nature. I have never missed a payment nor made a late payment and this is the treatement I receive. This is really BAD SERVICE! Your goal should be to retain clients not try and drive them away!