There are a few facts which need to be clarified before proper advices can be dispense.

1) sewerage and water piping are two different pipings and they should not mix. If you are certain that it is sewerage that's coming out from your floor, then it is rather weird that they would get CFO in the first place.

2) there is always warranty on your unit. But to be certain, you need to make sure that the root cause is not a bad neighbour who is clogging up the water piping due to throwing rubbish into the water outlet. If it is really the cause, you cannot sue the developer.

3) No point for you to see the director. If you feel that you have been "scammed" then sue them. That is probably the best way to get some attention.