Power BI - DAX

Hi,

I did not find Power BI community and even less DAX queries with Power BI... So I post here.

We have difficulties with the implementation of DAX queries on table joins/table relationships.
Microsoft support checked with remote session but told us that they are not expert in this area.. Who can help or how can we verify that this is not an implementation issue in power BI?. we tested moreless everything..

Thank !