From what you have stated on here, you no longer have permanent residency. Your parents abandoned their permanent residency and carried you along. Parents abandonment are reasonably imputed to minor children.

[Matter of Zamora](https://www.justice.gov/sites/default/files/eoir/legacy/2012/08/17/2796.pdf)
> **Children**
> 
> If an LPR parent is found to have abandoned his or her residence, and
> has taken his or her child out of the US, the parent’s abandonment
> will be imputed to the child. The child’s intentions are irrelevant –
> only the parent’s are, according to the BIA. Matter of Zamora, 17 I&N
> Dec. 395 (BIA 1980)



This is what will happen if you attempt to travel on your permanent residence card. First of all the airline in your country will likely prevent you from boarding because your physical card has expired. Even if you’re able to clear that hurdle, immigration at the airport in the USA have no choice but to admit you because abandonment is only determined by an immigration judge. At the airport immigration would charge an LPR it believed had abandoned his or her status under INA § 237(a)(1)(A) for being **inadmissible at the time of admission**. 

You will receive a Notice To Appear before an immigration judge who will make the final determination. From what you have provided it will be a formality, your permanent residence will almost certainly be deemed abandoned. At that point you will start accruing illegal presence which you will have to declare whenever you’re applying for a visa to any country whose forms ask if you’ve ever been deported or refused entry into a country.

To save you this trouble and out of an abundance of caution, the embassy asked you to formally abandon your permanent residency so that you don’t face the issues outlined above. They’re not telling you this because they think you’re still a permanent resident. It’s just to make your travels stress free. 

Save yourself the trouble, or alternatively if you have an appetite for risk taking, time to waste in immigration court, and spare money for an immigration attorney, attempt to travel with the card in your possession.