I assume that Evesham do not provide the credit themselves, the probably use a finance house like HFC or similar.
Evesham will have recieved full payment for the goods from the finance house, your agreement is with the finance provider to pay back the loan on the terms agreed. Although it is on 12 months interest free, you will probably find that the terms of the credit agreement are for a longer period of time, with a 'no interest buy out' option after 12 months. Are you simply paying the cost of the machine divided by 12 each month? or smaller payments with a lump sum at the end?
It way be worth checking the agreement that you signed to confirm if it is indeed with Evesham themselves, or with a 3rd party finance provider.
This is probably a good thing, as the finance provider will be jointly liable for the goods under section 75 of the consumer credit act.
Hope this helps,