We had exactly the same problem with leaks, two from toilets, and one in the wall; not to mention the set concrete in the sewerage drains, back door, which wouldn't open, cracked window.
It took the builder approx 3 months to send someone out. This was further to a number of promised visits (6 in total), where we had taken time off work to be home for.
The guy that came out to look at the leak leaned over the toilet to look behind, and then snapped the pipe connecting the cistern to the bowl, this put that out of action for some time; because the builder used a special size of pipe, which is only used on disabled toilets, we could not get a replacement, and he did not send another person out for a further 3 months.
I contacted Homebond, and they said that they could only recommend to the builder to sort the issues, and that there is no legal obligation on him to fix anything.
Is there anywhere where crooked builders can be outed to warn others about using them?
No other country would allow such cowboys build a lego house, never mind a real one!
Sorry, had to get that rant off my chest! but unfortunately, I think nagging is the only tool available to you.