Good afternoon. I am Loren, a licensed attorney, and I look forward to assisting you.
As you know, something which is too good to be true is, generally, not. Also, I am sure you suspect this is one of those times. Unfortunately, I am absolutely sure that there is no prize waiting for you from these people.
This is positively a scam. It is known as an "Advance Fee Scam".
1. You can not win a sweepstakes or lottery you did not enter.
2. No legitimate sweepstakes asks winners to pay upfront to release the winnings.
3. If they were genuinely holding money belonging to you should be able to tell them to just deduct the taxes, insurance, courier fee (all red flags, by the way) and send you a net check.
4. No government agency is involved in distributing sweepstakes prizes.
Do not send any money or otherwise respond. They are trying to steal from you.
Here is an online warning from the FTC: