If there was an agreement as to services and price/compensation, that agreement was a contract. Contracts, even if they were oral (that is, unwritten; "oral" is the correct term, not "verbal") are enforceable in court: you could sue, such as in small claims court as your own attorney, for "breach of contract"--if you did your part (created the content requested), they are contractually obligated to pay you the full, agreed-upon amount. If they did not, you could sue for the difference.