Received "Threatening" SMS

I just received a disturbing sms from Nedbank with regards to one of my accounts, not even sure which one as I have not used any of the accounts left open with Nedbank for quite some time now.

I do not know what is going on and to receive a SMS saying: "A Notice Of Demand has been sent to you. Please rectify your Nedbank account within 24 hours or contact ***urgently. Ref ********** 00"

I tried calling the number given and it either keeps me on hold for minutes or it drops the whole time so what is up with that as well.

I emailed the contact centre but knowing their turnaround time nothing is going to be done until Monday.

I do not know what this is about as I never received any Letter of Demand as the sms states, so what must I do.

Now I am glad I have moved from Nedbank because I have had more problems with them than any other bank I know of.