Bizarre Vodacom credit rating

I have an existing data account with Vodacom for a monthly amount of R200.

I have ported my cell phone and iPad sim from MTN back to Vodacom because of poor MTN reception in my area.

The increase in the credit for sim only contracts I require is a maximum of R400 per month.

VODACOM HAVE INFORMED ME THAT MY CREDIT RATING IS INSUFFICIENT TO JUSTIFY THIS INCREASE IN CREDIT; MY CREDIT RATING IS ON THREE CREDIT RATING COMPANIES AND IS EXCELLENT.

Vodacom have told me that I must contact Experian to resolve this issue! Experian have failed to respond to three requests to clarify

How do I now find out why my credit rating does not justify this increase or, alternatively, why can the issue not be resolved with Vodacom as there appears to be a serious error here.

This is unpleasant and annoying at my age; any help in resolving to this would be deeply appreciated.