Cornetto complaint: Piece of wire found in a Cornetto ice-cream

While on holidays with my wife and son in Portugal last year, I bought a box of cornetto ice creams in the local supermarket. The following day, we decided to eat one each at the pool. I took a bite out of my ice-cream, and felt something wire-like in my mouth. I reached in and took out what appeared to be a small piece of copper/brass wire, possible a staple of some sort.
Fortunately, I didn’t injure myself. What was even more fortunate though was that I ate that particular ice-cream, and not my three-year old son, who had another Cornetto at the time from the same box.
When we arrived home to Ireland, I phoned Unilever (the manufacturer) and explained what happened. The asked my to email them, outlining all the details, including a picture of the wire (which I had kept), and the barcode from the Cornetto box. They subsequently asked me to mail on the actual piece of wire, which I did.
After several weeks of updating me to inform me that they were carrying out a thorough investigation, and thanking me for my patience, they finally responded as follows:

Upon inspection from the quality department at our manufacturing unit, they have ed that they thoroughly checked the production line for any possible points of origin and can that the foreign matter you found has been identified as a staple. They have ed that they do not use staples anywhere within the facility.
Taking the above into consideration, our investigation has concluded that we are unable to definitively the origin of the object you found. We will continue to investigate internally with our suppliers, however, we would like to conclude your case and offer you a resolution by way of a cheque to the value of £20.

So, they can identify it as a staple, but will not claim any responsibility for it being in the ice-cream, so are offering me £20 for my trouble! I cannot but feel that they are either covering up a glitch in their production process, or, they just don’t believe me. Either way, I fell very aggrieved by their response.