Request of payment when I am a third party?

4years ago whilst employed/contracted as an engineer on a vintage car project, I suggested that I knew a parts supplier of second hand spares of the type required. The arrangements were made by the owner of the restoration co. to purchase items. I offered to collect these. On arrival at the supplier most of the order was ready for collection except for some small items. I was offered a selection of these items in a box to sort through as those ordered had not been collected from the box. The agreement was that I would list all items used and the remaining returned when no longer required.
When the work was completed many months later all of the particular small items were listed for an invoice and the remaining packed on to a despatch section to be returned by the restoration company owner.
Over three years later I (third party) have had a request for payment (a guesstimate figure of £1400) from the supplier. I informed him that the parts transaction is with the restoration company who said they had returned the item with the list of used parts, but no longer had despatch records of this.
As a "goodwill" gesture to protect my reputation, I have offered to provide my skills to the supplier in renovation of some items for his stock for little or no charge.
This was ignored for 6 months until a recent email asking for payment and suggesting that my "goodwill" offer is not appropriate.
The supplier appears reluctant to contact the restoration company even though I have stressed that all transactions were with them. Many thousand £ of parts were bought and sold between the two companies during the renovation, all without problems.
It is also a surprise that a three year period elapsed between the collection of the small boxed items and the verbal request for payment? There are no PO or Invoices raised for the items.
Please can someone help with advice?

David,

Thank you so much for your time and trouble. As you mention no PO was signed and I have asked for an invoice No. (no reply).
Although I feel that I should not have a problem I feel sad that I may be involved in such a dispute so unwittingly.
I will keep you posted as we progress, thank you so much.
Eric..