Ground floor flat flooded from main drainage pipe, management company refuses to fix

I have a ground floor flat flooded from main drainage pipe, where the waste water came backup from the main drainage pipe up to kitchen floor and sink while no applicant is used in my flat.

The management company sent a contractor who tested and said the main damage pipe is clear (simply by running dye through) and

refuses to fix it.

We know the main drainage pipe is not 100% blocked as everyone is using the drain on daily basis but likely blocked enough to floor my ground floor flat. Their test and conclusion were almost pointless.

How can I make the management company to instruct a competent contractor to fix the problem?

My flat is now subject to flooding at any time.