Here's an old trick to get out the cork once it's been pushed into teh bottle.
First decant the whisky into a glass not plastic jug
Second take about a 30cm [12inch] piece of string, put the two ends together and push the loop into the bottle.
Third invert the bottle so the cork drops down to the neck lengthwise. Flip the loop over the cork, then pull smoothly.
The cork should come out witha little finagling then empty the bits out of the bottle, rinse, dry, return the whisky and cork [with a white wine cork if possible] but never let the whisky touch the cork.
If you're like me then there's always a nearly empty bottle of whisky that I can help on it's way, if so then just use that one.