Distinctcount excluding negative number through time

Hello!

I am quite new to Power Bi and I am currenlty experiencing trouble with the DISTINCTCOUNT  function. 

What I am trying to do is quite easy, counting the distinct number of customer excluding the negative and nul numbers. 

My formula is the follwing: 

calculate( distinctcount(Database[Parent name]),filter('Database','Database'[transaction sales]>=1), filter('calendar','Calendar'[Year Type]="This Year"))

 

My expected final visual must be as followed

However for some reason Power Bi count the customers as long as they have a positive amount once. Which results in a deviation in the final number of customers per month. 

I don't know how to chnage my formula to make Power Bi iterate on a monthly basis not on the total. 

 

If any body could be of assistance on this point this would be really really helpful. 

Thank you in advance 😣