as far as i can remember, i've only had to use customer service on:
bet365
chandler
bluesq paddypower bet365 by far the speediest, most helpful etc etc
chandler and
bluesq were both fairly trivial inquiries, although
bluesq refused to settle a large bet i had with them early, but customer service was prompt enough and polite enough
paddys are very good, always seem to resolve queries in punters favour, or at least that was my experience and from big brother tales it is others too