A verbal agreement WILL stand up in a couurt of law, there are cases proving it. If I were you I would go to a company called thomas higgins, who are solisitors come debt collectors. Open an account, it costs nothing and while your doing this send a stroppy letter to the manager of the shop, telling him that as your invoice is now late you will give him seven days before taking further action, and passing all subsequent cost on to him. Once the seven days are up just fill in the bits online for thomas higgins and they do the rest. The first letter they send is only £2.00 + VAT so it doesn't break the bank, and you will be amazed how quickly that cheque will be in the post