Telkom demand payment without invoicing - struggle bookeeping?

I've received an SMS from this captured institution, claiming that I have to pay them R 900 +. I do not dispute that I owe them, as I have owed and paid them for the past more than 10 years - but at least, supply me with an invoice!! I have tried their website, their portal, their contact details - NOTHING, ZILTZ, NO-ONE to supply me with invoice or even an apology or promise that such document will be forthcoming. Since when can a state owned company demand x amount without giving a reason? Oh, sorry, I forgot, this is a decolonised African democracy - everything goes to the connected.