Blacklisting of a phone not used on Vodacom

I bought a Samsung S4 from Mr A Graaff on 19 September 2013. This was a Vodacom phone which I have been using on MTN since then. On 28 May 2015 the phone was blacklisted. I was informed by Vodacom that the account I*** was in arrears and they can not unblacklist the phone until the Vodacom account belonging to A Graaff was paid in full. At the time of purchase, Mr A Graaff gave me a copy of his drivers licence as well as his phone number ***) which no longer works. I have given Vodacom copies of all of these documents together with a affidavit stating that I am the owner of the phone. Vodacom refuses to unblacklist this phone until A Graaf has settled his account. Please can somebody help me.