Getting compensation out of the railway is not as straightforward as it might be. Some of these points might help, but my apologies if they are things you have already thought about:
- Are you claiming for a delay, or a refund for having to abandon your train journey? The way you claim is different.
- you will be claiming for a delay if (as mentioned above) your train ticket covered the whole journey, and you didn't have to pay again to use the bus (on your way to Peckham Rye) or to get to Victoria on your way back. If it's a delay, then you claim from the train company who caused the delay - which in this case is London Overground. You will need the TFL 'Overground and TfL Rail delays' webpage.
- you will be claiming a refund if you ended up having to use (and pay separately for) some other form of transport to get where you were going. For this, you will need to go to talk to the ticket office at Aldershot.
You have already had one go, and you may have applied to the right people in the right way. As they seem to have come up with the wrong answer, you are able to appeal. Their current reply probably tells you how to do that. So use the appeal system to tell them what you have told us - and this time you may get a more sensible answer.