Aggregation on a Header-Details Model

[kostaszogo21]

Hello guys!
I'm in a really bad situation and i would appreciate all the help i can get from power bi ninjas/gurus out there.

I am working in a project that seems to be above my skill level (i've been working on powerbi for less than a year) and what i have at the moment is a model that i've never seen before.
Think of a Telco's call center where the customers enters the first (automated) system of the call center (auto_calls) and if his/her issue isn't solved then he/she is re-directed to the second system (agent_calls) where he gets to talk with an actual person/agent.

But in each of these systems, on the first "section" general details about the call as a whole is gathered (key_id, A_number, date etc) and on the second "section" more info about the specific steps the client is entering is available (ex the client talks with one agent and the is sent to a second one and so on). That's why i'm having two sets of header-details table.

So, the model looks like this:

The initial request from the customer was to be able to track every single call (and all of its details) for one year, that’s why we have used the above approach/model.
And everything has worked fine. But then a second request has been made from the customer.
Besides the initial request, the customer wants another set of dashboards, that shows only aggregated per month data, but this time for two years.
We can’t expand the initial model (shown above) to two years and then show the data in a monthly basis, due to size limit, so we have to find a way to keep all of the info shown in the original model and expand it for two years, without increasing the size.
So, I guess, we need some kind of aggregation. But how is that possible when we “need” the detail info of every call?
Let me explain. If I had one row for every call (like in the auto_calls and agent_calls tables) the aggregation would be possible (probably with SUMMARIZE COLUMNS i guess). But the info in the details tables is of a more detailed granularity (ex one call can occupy two agents) and it can’t be shown in a one row-per call level.
I am in a dead-end here and I hope somebody comes up with an idea about my problem.

Any idea/proposal is more than welcome (the community is my only hope)

Thanks in advance guys 
PS: Unfortunately, i don't have the permission (by my forum rights) to attach the pbix file. But if someone thinks of a solution i can email it to him/her

[kostaszogo21]

Thank u for the guidelines Ibendlin.
Here are the links to the sample data
https://docs.google.com/spreadsheets/d/128hQFic0DSYIbVdiyWclfl5KhtpwTTlj/edit?usp=sharing&ouid=11086...

https://drive.google.com/file/d/1imM9zZRjODhHTNhXrjCHj_tWhJcMNrUz/view?usp=sharing

Hope this helps,
Best Regards,

Kostas

[lbendlin]

Please provide sample data that covers your issue or question completely, in a usable format (not as a screenshot).
https://community.powerbi.com/t5/Community-Blog/How-to-provide-sample-data-in-the-Power-BI-Forum/ba-...
Please show the expected outcome based on the sample data you provided.

https://community.powerbi.com/t5/Desktop/How-to-Get-Your-Question-Answered-Quickly/m-p/1447523