Vox Telecom management decision

I am interested to get a response from vox telecom regarding their pricing options. They are running a special on their 100gb internet service for new customers. Existing customers are not allowed to change to the new billing option, instead they must pay more. However existing customers are not on a contract they are based on a month to month deal. Therefore it is possible for an existing client to cancel their contract at no expense and re apply for the new deal. My question is why would you alienate your existing customers irritate and frustrate them and put them through totally unnecessary admin if it is possible for them to change anyway. Honestly I really want to understand this business decision. Furthermore I don't even know if it is legal to change your tariff structure and not offer the option to new customers based upon icasa regulations. Please can someone explain this situation to me.