You are going a bit off-track.
The contravention is for waiting on a single yellow line, for which loading is an exemption.
It isn't a bay as such.
No need to talk about the bus stop which is nothing to do with where you were.
A single yellow line must either have its own timeplate, or be controlled by an entry sign to a controlled parking zone (CPZ). I can't see that there is a CPZ so I suspect the line might just as well be an unrestricted bit of kerbside and a botch by the council after changes along there (probably should be a double yellow).
Wait for others but the below is what I see.
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Dear Chester,
I am challenging the PCN on the grounds that I was either:
1. Carrying out the exempt activity of loading
2. Or that the contravention cannot have occurred.
On 1., I am a xxxxx and waited on the single yellow line for the purpose of unloading x equipment to y, which entailed xxxx and took only as long as necessary. I enclose evidence for this.
On 2, there is no timeplate for the single yellow line and I am not sure it is in a controlled parking zone. If it is not in a CPZ, the contravention cannot have occurred.
I trust you will accept my challenge and look forward to your early confirmation of cancellation.