What size batch is it? 10 teaspoons of sorbate sounds like a lot to me: I've usually read to use less than half a teaspoon per gallon.
I 'think' sorbate requires metabisulphate to be added too to be most effective. Meta actually stuns the yeast instead of just preventing it for reproducing. Or maybe the other way around... Either way, it's advised to use the two.
I've also heard that it's pretty hard (bordering impossible) to stabilize wine whilst it's still fermenting healthily. It might turn out that you have to let it dry out.
If that's the case, I'd advise you make a note of the gravity and ABV you liked it at, and formulate the recipe around that in future batches (i.e. ferment dry to the ABV you like, THEN stabilize and back sweeten to 1.028). If you wanted it sweet (which it sounds like you do) then champaign yeast probably wasn't your best choice.
Some people may recommend stove-top pasteurization. I don't like this technique but it's something to consider if you're desperate.