My apologies for being slightly inconsiderate, and also for creating something of a misunderstanding.
My dispute was that some staff locally appeared to have been trained to count the vouchers last, rather than first, to the effect that no change was being given at all on any transaction that involved a voucher. Having established that this wasn't right, I posted about it on here and contacted Customer Relations. They did nothing to really resolve the dispute because they didn't admit that any mistake was made, insisting, as people have correctly done in this thread, that there is no change from RTVs*.
They sent me a free travel voucher 'as a gesture of goodwill' that I neither want nor need, but neither did I want or need my 7p anyway. So I'm neither up nor down, but there are no doubt still people getting it wrong that I can't do anything about, this is what annoys me and occasionally results in these misunderstandings.
* If you do think RTVs are a sensible and appropriate way to issue refunds / compensation, not giving change is the only way to deal with them. Although what I do think is neither sensible nor appropriate is for some TOCs to issue them without rounding up to the nearest five pence!