I have a Generation high D that is awful !!! 
The low notes flip up to the second octave far to easily.
can anyone recommend something ?
Did you do the blue tac tweak?
YOu can also get a very small screwdriver very slightly bend the blade upwards or downwards a tad. Or sand on the end a bit, and although that may be the tweak you need, more whistles are ruined by sanding than any other way.
You might look at the beveled windway tweak too. Do a search. MOst all of these tweaks have been discussed at length at one time or another.
Read the tweaking instructions on the main C & F site - it goes into detail, and usually works quite well.
A quick check you can do - look at the whistle head to see if there are any tag ends of plastic on the interior (windway, blade, sides of the slot, etc - if so, cleaning them up (carefully!) with a sharp knife will probably make a huge difference. Try that first, then if necessary try measures like careful sanding/filing, sticky tack under the windway, etc.
Even the worst Generations can usually be made quite playable, and a significant number end up as Really Good Whistles.
Despite their out-of-the-box QA problems, Generations are my favorite cheap whistle. If I didn’t want to tweak, I’d probably prefer Sweetone D’s - I like the sound of a Generation better, but an out-of-box Sweetone is much less likely to need tweaking to sound OK.
I have removed all the excess plastic and I sanded a little but off the soundblade!
It still flips up too easily. 
What is the thing with the blue tac 
There is a little cavity or chamber under the windway . Fill it in with blue tac until it is level with the windway exit. It will stabilize the tone. It helps a lot.
OOoh, don’t know how much that bending the blade thing helped anyone else, but it helped me fix my oversanded C whistle! YAY! Thank goodness for my nosyness :roll: