Cannot access API although everything correctly defined

Using DataTables 1.10+ and cannot access any API functions.
It always returns with .... is not a function

So I have my datatable, which I initialize with a local and empty dataset

So far so good.
Now I want to change the data by calling the API through
datatable.clear();
datatable.rows.add(newDataArray);
datatable.draw();

However, not matter what function I try to call with booked_events_datatable.clear(); for instance, it always throws js error:

I even check if the my datatable object is really availabe before calling clear()

result:

Is it an issue that the table id is the same value than my table js var

Should'nt be, right? So what else is the issue here?
I spent hours and could not find the cause for this weird problem.

Please help.