How common is it to hear a singer sound the same no matter how much they try to sound stylistically correct in another style?! This is especially true of classical singers because our singing is more academic and must be correct or "better" than any other style, right?! I studied how many years only to accept that classical singing is not better than any other singing? More academic does not mean better!
What to do:
Close your mouth and just breathe like you would while asleep. Now, VERY SLIGHTLY part your lips and start talking. It WILL sound nasal. You WILL have a HIGH LARYNX. Everything that you're taught was "wrong" will be present in the sound! Shakespeare's Hamlet "There is nothing either good or bad but thinking that makes it so."
Here is basically the brightest, most closed sound you can make. I say closed because it's the "tightest" your vocal tract will be. There is very little space for your sound. From here, start speaking/singing in the sound. You likely won't like it. SLOWLY AND MINUTELY, start opening the tract until you reach full openness.
You can think of these as levels of openness. You can think of it as characterization of the voice. For classical singers, you're literally going from chiaro to oscuro!
Once you've found the setting most appropriate for your voice/style, start to make your sound your own. Make it darker/brighter, sing with more closed/open lips, sing with more/less air, etc. Anything to help make it YOUR sound and not something artificial!
If you're having trouble, then really try to copy other people in that style until you've figured out what they're doing. Once you can copy, make it your own!
And that's it!!! :D MUCH easier said than done, but all the work you put into yourself will make it that much more valuable!!!
"I do not know anyone who has got to the top without hard work. That is the recipe. It will not always get you to the top, but should get you pretty near."