Vodacom's ********* business practises regarding debt collection

I recently left Vodacom and moved onto Telkom Mobile. Since then I have been contacted by two companies MBD and Hammond Pole attorneys regarding debt collection on Vodacom's behalf. I have requested an official invoice to show what it is I'm am paying for and neither of the two companies can provide me with this information except a bank account number and an amount. There is no ways I'm going to make a payment to a random bank account from some random email address that has no credibility. MBD has called me several times repeating the same song but can't provide me with an official invoice as to what it is I'm paying for. My point of concern is that my details have been handed over to two different companies asking for money. This is very confusing and seems very *********. Both these debt collection companies are incredibly rude on the calls. I have since tried to phone hammond pole but their line appears disconnected. Google reviews also show that the company is up to no good. I will not make any payment unless I have an invoice to show what it is I am paying for. This is what I have told both debt collection companies but yet I still receive the same calls telling that I owe Vodacom money. This is very ********* business practise and the very reason I left Vodacom in the first place. I'm sure many South African citizens are aware of the 'OUT OF BUNDLE CHARGES' mess that has been going on with Vodacom. I would love to remove this company from my life but unfortunately I can't make a random payment into a random account without any credible invoices. Vodacom should take responsibility and communicate better with EX clients regarding money payments and the settling of accounts. Could you please also explain why I have two debt collecting companies calling me almost daily. Surely one company is enough and what happens if I pay one of the companies, will the other even be informed or will I still receive calls from this company? Both MBD and Hammond Pole are not aware that my account is in the hands of both companies. It just seems like there is a problem here. Good luck to future and current Vodacom customers.