Wow, great guys - thx for Your help
Regarding the photos on bmxmuseum I'm not sure about the "Aero Foxbat"...
As You can see in the following photo of a Aero Foxbat (1984) it has a cross-beam behind the bottom bracket - but my frame has not:
Same on the following Foxbat's (also 1984):
And the shape of the rear drop outs seems to look different - more straight and not so curved:
Maybe it could be an "Aero Pro Foxbat" like this one (hard to see):
But I've found a photo of a Pro Foxbat; but it also looks different in my eyes:
Now I've found much more bikes with nearly the same frame...
Like the 1985 Nova Freestyle:
The 1986 Supercycle Bobcat:
And the 1986 Jetter Freestyle:
Aaaarrgghhh,....
For me particularly the rear drop ends always looks different to the frame I have - or am I wrong?