After sales service/Upgrades

<p>I am a Vodacom customer now for more than 10 years, last year April I took an upgrade handset (samsung 7 Edge) through Vodacom call centre, subsequently something went wrong with the handset, according to Samsung Customer Service I require a Tax invoice stating that this handset belongs to me, which makes totally sense, I am now trying for two weeks between upgrades and After Sales Service departments to obtain this document, many hours on the phone with various call centre agents, promises, I sent emails to the upgrade department which I can see they open but to no avail, They keep sending a document stating upgrade equipment quotation, I cannot do anything with this document. It does not prove I am the owner of the phone. Can someone please give me an idea of what to do, bar cancelling my contract with Vodacom.</p>