Final update.
Following the sales managers investigation, he was initially unable to resolve this matter and passed the blame back onto mobility.
Following another few emails, I instructed him to pass the complaint to the managing director. And finally, after careful consideration they agreed to honour the original AP and throw in a full tank of fuel.
I would like to thank everyone who offered advice on this thread…. it just shows the power of the forum to help resolve matters. ??? A big shout out to glos guy for the draft he formulated.