Especially as I now know by phoning them they were accusing me of staying over time - which I didn't. I really need to address that also.
Not really, if they reject the informal representations (which they almost universally do) you get another chance at the formal stage. Also, given the timings on the clock and the time stated on the PCN, we basically know you can't really lose this case as long as you don't miss any of the deadlines, so I wouldn't worry about it too much.
You must also remember that the people who answer the phone are not trained appeals officers and they're giving you information based on their own guesswork / interpretation, and nothing that is said on the phone can really be relied upon. It would be more helpful to get an informal rejection that tells you you've overstayed, once you have that in writing you can use it at the next stage to make the point that their argument is flawed.
