Incorrect invoice

As per previous request, my account was credited due to an incorrect charge. However I still receive invoices on this account every month with the wrong amount and have to request another credit again. Why can it not be fixes on the system once and for all? I simply cannot run to Hello Peter every time, but Vodacom leaves me no choice since this is the only platform where I actually receive help! This is absolutely pathetic! I cannot wait for my contracts to expire so I can change from service provider.