Thank you for using JustAnswer. I am Loren, a licensed attorney, and I will do whatever I can to answer your question.
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 legitimate lottery or sweepstakes notifies major winners by text, FB message or regular mail.
Do not send any money or otherwise respond. They are trying to steal from you.
Here is an online warning from the FTC
You can also file a complaint online with the FBI at www.IC3.gov.
I hope this is helpful to you. If you have follow up questions feel free to ask. It is never a problem.