I had boost creep problems with my old K1 when I installed an Aussie DP with no cat. Common problem with such a setup. Assuming it's an actual creep (not overboost). Difference is it'll hold the correct boost for a moment, then creep up with rpm/throttle in the higher rev range.
 
Solutions below:
 
Port the wastegate opening
Restrict the exhaust (add a cat or smaller 2.5inch dp)
 
I added a cat (to help with the legal aspect too).

No it's creeping... I've experienced the overboost before and realize how it works, but this is different.....it will just creep forever and won't stop....even on factory boost (tried unhooking the electronic boost controller aswell).... So now I'm wondering what I should do in order to fix this problem.

Cheers

First thing to do, take the dump pipe off and look indise where the collector is for scrape marks of the wategate flap hitting the dump pipe.
You could be experiencing what some others here have described, waste gate jamming when opening, could be jamming half way through so instead of the exhaust gas bypassing the turbine its making it boost more but just enough to cause creep
That’s where I would look first for sure.
 

Ive just fitted a berk dump pipe to my gen2 (sourced from Gorilla Industries) with no issue except for a modest increase in boost. Before you go removing the dump pipe again check and make sure you havent disturbed any hoses etc. The reason might be simple.

Jay has pretty covered every aspect for boost creep (ie. the boost will continue to go up beyond the set level due to the wastegate not been able to bypass enough gas to control the boost.) Most common causes are:
- the wastegate not been able open properly (either by obstruction or not enough travel from the actuator)
- Not enough wastegate flow (wastegate port too small to flow, or too much turbulent flow for the wastegate to operate correctly, which is why some people have a divider.)

If you are able too, the first thing i would do is connect a hose to the wastegate to a pressure source that you can try with the engine off, hell even a bicycle pump. Pressurise the wastegate actuator and make sure it moves in a full range freely. If you notice it gets stopped or doesn't seem to travel very far, it might be time to take the dump off and check nothing is getting stuck.

If it all seems good, porting the wastegate port might be an option, fitting a divider or putting a slight restriction in the exhaust may help.

No extra solutions to offer, just an order to attempt things.