Fraisse: Yep, did this myself and eventually got the miles, but very ungraciously. Throughout I was made to feel like it was a big favour, irregular practice, I was uptight even pursuing it, etc. Makes my blood boil that in many companies this sort of attitude now appears to prevail - "Oh, we didn't do as obliged, but aren't you sad to waste time pursuing it?"
Took ages to chase the first two and now Avis UK have deftly deflected the latest claim to the rental location. UK absolves itself of responsibility and invites me to chase MRU for an overcharge and 1,500 missing miles. Shocking.