Vodacom voucher not the value stated

I am trying to query why a VodaPay voucher for Krispy Kreme, for R25 only gave me a discount of R17,50. On the Vodacom Twitter feed, I am now being asked my account details, my payment plan, my email address, and more and more. BUT NO reply as to why I did not receive the discount as promised on the voucher! Rather than admitting that there was a problem with the value of the voucher received, your Twitter person seems to be making the issue all about ME. Asking me my account details, my contract name, my ID, my email address. I feel completely uncomfortable giving all this information! I would SIMLY like an answer on why I did not receive the value of the voucher used - plain and simple - Vodacom issued a voucher of a different value to what was stated on the SMS.