how & where to complain about plumber's job?

the ceiling of the neighbour downstairs was leaking so we got the building guard (minimal english) to get a plumber (no english) for us. with the neighbour (minimal english) on our back, we said ok for the quote of $13K for fixing the pipes and the ceiling of the neighbour downstairs.


at that time, my husband (no chinese) was at home and the plumber had said (through the building guard) that he will have to change the internal pipes as well as the outside pipes and the job will take 2-3 days, that's why the quote is $13K.


plumber came on friday and basically changed the pipes in the bathroom and the kitchen. i was at work and husband was at home monitoring what the plumber was doing. i asked my chinese friend (on the phone) to ask the plumber how come he hasn't changed the outside pipes and he'd said that there is someone working on the outside pipes but my husband didn't see anyone working on the outside pipes! my chinese friend also told the plumber that he'd told the building guard that he will have to change the outside pipes and will take 2-3 days but plumber said that he didn't say anything like that and husband was probably told the wrong thing by the building guard..?!! lost in translation!!


when i got home that friday evening, he had done the job - well, just changed the bathroom pipe and kitchen pipe. i did ask him (minimal chinese) where his other colleague was? he said that he did it himself (which doesn't match to what he said to my chinese friend on the phone) and asked for the payment, which i paid reluctantly.


today, the neighbour downstairs came to check his work (dont know why?) and he said that plumber ripped us off as he didn't do anything about the outside pipe (the neighbour was there while plumber was talking about the fixing job).


do i let it slide or do something about it? what would you do?

thank you for your replies. i'll get a chinese friend to confirm on what was told to the building guard first and go from there. my husband probably misunderstood (?) so i better back the complaint by the building guard since he was present at the time the plumber was talking about the repair job.