But does Spondon have it's own, specific, railway station?
Yes it does, it's operated by East Midland Trains.
In the Derby area Spondon is much like Parson Street, Filton Abbey Wood, Lawrence Hill, Stapleton Road and others in the greater Bristol area,
These are all stations that commonly figure in short-fare and ticketless travel reports and the TOCs, Transport Focus and ultimately the Rail Ombudsman will be aware of this..
But in the context of your journey and being questioned on a ticket, Derby isn't where you travelled from
Exactly.
I know that this will upset some people, but to be perfectly blunt and although he is absolutely entitled to do so, I believe that suggesting that the OP now pursue a different complaint may be akin to 'tilting at windmills'.
Readers have only the details posted here to go by, I'm not saying the OP has intentionally withheld anything, but any further examination will be based on the process and how it was resolved, the fact that the OP had opportunity to debate and ultimately agree settlement terms and will correctly look at the evidence held by both sides. Here on the forum readers have not been a party to all of that.
By all means, the OP may exercise the right to complain.