New VS existing customers

I wanted to upgrade my data cap on my fibre contract that I have with Vodacom.I phoned in and got a quote which said that my new amount will be R849 for the package that I want. When I received the acceptance documents, it did not reflect the amount of the quote. It now said R899. I phoned in to enquire about this, and after several attempts with several people it was explained to me that this price only applies to new customers. I did appreciate the last consultant explaining me what the misunderstanding was and that the other consultants are not informed of this. It is however very disappointing and quite shocking as Vodacom would rather rope in new people than look after loyal customers who pay their bill every month. Vodacom is already the most expensive provider that I have ever used, so it would not take a lot to move to another provider after my contract end. Why is this approach followed, and does it really help to grow loyalty of your customers in the long run? I would like to invite Vodacom to explain to me what their reasoning behind this is, and whether they are at all interested in keeping me as a customer. I dare not say what this feels like to an existing customer. I think my complaint speaks for itself.