There may be a trap in the sewer line that leaves the house and joins the main sewer line. It may have become clogged causing a backup that floods the basement. I clear it by reaching down into the trap and manually cleaning out the goop.
In the basement of my house, there is one pipe that carries the waste water of the entire house, leaves the house, and goes out to the street. I have an access point, where it leaves the house, and I can open the trap and clean it out. The trap in my house gradually gets clogged and I periodically have to clean it out.
we had a simular problem we has somebody come down and waterproff the bricks that was all around that back drain cuz when it rained very hard it would back up and hit the wall and go into the basement
we also pay a yearly fee to the sewer company they come down a couple of times a yr and do preventive cleaning in drain in bk of house and in basement main sewer