Email address not changed after 4 requests

I have 2 Vodacom contracts. Five months ago I made a request via the call centre to please change my email address. I wanted them to delete my work address and send my statements to my personal address.The first month after the change Vodacom sent one statement to the old address and one statement to the new one. I was ok. I phoned in to get that rectified. The 2nd month the same thing. Every time they promise that they will change it on the back end system as well. I was happy and waited for my statements. Again the third month they send one invoice to one address and one to the other. How difficult can it be to send both my statements to one email address? I phoned in again (holding forever and ever..) Again I was promised that it was definitely changed and I have no need to be skeptical as both statements will definitely be sent to my email address of choice. (Now changed for the forth time.) What a surprise when I receive my statements yesterday! One statement to the one email address and one to the other. Please let me know how many months I still have to do this? I need to work out how much time I will waste and prepare myself emotionally & mentally to do this over and over!