We bought a house and we moved in last month April only after 2weeks of our stay the drain system started to flush back waste then we reported the issue with the office as they gave us a period to report any issues that is faulty it will be fixed now they

We bought a house and we moved in last month April only after 2weeks of our stay the drain system started to flush back waste then we reported the issue with the office as they gave us a period to report any issues that is faulty it will be fixed now they are giving us hard time to fix the problem. Remember drain saytem of a house there is toilet in the waste guys I have a 3year old daughter it is not healthy in the situation I'm in. Now we are being told to go to the municipality they say the blockage is in the mainline. How can it affect only one house if the problem is from the mainline