Two 90 degree elbows in sewer vent pipe

I recently had my old cast iron sewer drain stack replaced with PVC. The plumber installed two 90 degree elbows on top of 4” main drain line in the basement with short wye connection in order to connect vent pipe that was offset. I have a toilet, shower and sink on floor above the two 90 degree fittings. I am now experiencing gurgling sounds when toilet is flushed … and if I fill the sink with water and then drain, I hear air venting through the toilet. How can I fix this issue ??? Any help is greatly appreciated.