Lumia 800 APN error

[great general]

Hi, I wanted to ask this so that I could see if anyone else had similar problems.

I've bought lumia 800 recently and updated it to 7.10.8862.144
The phone was bought in germany but I am using it now in croatia.
Anyway, everything worked fine up until a few days ago when the 3g internet wasn't synchronizing and so I checked the forums and found that I have to edit apn settings.
Since my carrier is t-mobile croatia I wrote down web.htgprs under settings and then everything worked fine again for a couple of days.
After that everytime I enter IE under E/3G it redirects me to a page that says that my APN settings are not ok.

After that I've tried everything, and finally I've reset my phone to factory settings but still no luck. It still redirects me to this page that says that my apn settings are not entered.

What do I do?????

(Other than that a really great phone)

 

[stmav]

Have you contacted t-mobile Croatia? Maybe it's a carrier issue or setting.

 

[great general]

about 10 times allready, they say it's not their issue but a phone problem.
They've directed me 10 times to input apn settings and turn the phone on and off.

 

[great general]

Recent updates: At t-mobile they told me that the real problem is that the phone was bought in germany. So everytime it tries to connect it tries to download apn settings that were made for their carrier.
They told me I should try to install croatian t-mobile settings for the phone, but I haven't found any way to do this on the internet.
Anyone have a clue?

 

[great general]

Also one more question: Would this solve my problem?

HOWTO Debrand your Nokia Lumia 800 - Giffgaffers g... - The giffgaff community