A good first step is to recognize that a contract cannot grant any party the right to unilaterally alter the agreement in
any way. Next, recognize that no contract may be applied after the fact (especially shring wrap agreements), the deal is whatever it appeared to be the moment money was handed over. By default, that is assumed to be a sale.
Next up, we need to address the multi page walls of text. Start by re-considering the liklihood that the customer actually understood everything in it and limiting it to what an average person would have understood. Nobody should need a lawyer to understand a cellular agreement or buying a piece of software.