Is the sewer from the apt block blocked or is it okay?
Who has paid for the work before?
My experience that whereever the blockage is has to pay for freeing it up
Our row of houses had an issue where a new owner with a house full of babies and young children, who was the first one on a row of four, was putting baby-wipes down the toilet and they continually blocked the main manhole which is on my property.
I was paying 160 euro to have it cleared.
We never had an issue for 20 years until they arrived.
They denied all knowledge and told us to go...
The 3 adjoining neighbours installed a CCTV camera in the first manhole off their property and collected several days of continuos footage, put it on a a series of dvds and dropped it in to them.
End of blockages.