The general rule in contract law is that a written contract normally takes precedence over any verbal understandings or other agreements that are not written into the contract. Although you say your contract did not contain any notice of verbal agreements or contracts, just because those words were not used may not mean the contract does not address them in a way which specifies they are not to be considered part of the contract. Many contracts include a provision in them indicating that the contract, as signed, is the "complete agreement" of the parties or other words to that effect which are normally interpreted to mean that there are no other "agreements," "conditions," or understandings between the parties.
Many persons do not realize that when they sign a contract their "rights" mainly are those stated in the contract itself. In most cases, unless a consumer protection law or the circumstances of an agreement prove otherwise, therefore, the right of a party who signs a contract are those specified in the contract and not those which may be spoken about or discussed either prior to or after signing a contract. This is one of the reasons why it is so important for people to fully read a contract before signing it, even if the party who gives them the contract to sign explains the contract or otherwise indicates what it "says."
However, in certain situations, there may be an ability for a consumer to require a retailer to abide by other promises or agreements made, particularly if a consumer has been mislead or a retailers has misrepresented information about matters to a consumer. It will depend on the facts involved, and a written contract may prevail in most situations, but it is not a guarantee.
Every state has consumer protection laws which consumers may learn about through contacting either their state's attorney general's office or, in some cases, a state has a "consumer protection" office or bureau that handles such matters. Consumers can normally contact their attorney general's or other consumer protection offices to discuss problems they are having with retailers, service providers, or other businesses to obtain information on what they can do and what protections they have under their state's laws and to, if they wish, file a complaint against the business that may then have the attorney general or the consumer protection office investigate the business and/or situation.
If you can tell me what state you are in I can provide you with a link to your state's AG or consumer protection office.