What is the ruling on continuing membership in pyramid schemes if the company enrolled the member in its pyramid system without his knowledge, some time after his initial subscription?

It is not permissible to participate in pyramid schemes due to their inclusion of gharar (excessive uncertainty/risk), maysir (gambling), and consuming people's wealth unlawfully. If a company enrolls someone in such a system without their consent, it is not permissible for that person to continue in it, because continuing in a void contract is like entering into it from the outset. This is supported by the Prophet's (peace be upon him) abolition of riba (usury) from the pre-Islamic era, and Allah Almighty's saying: "So whoever receives an admonition from his Lord and desists, he may have what has already passed, and his affair is left to Allah. But whoever returns [to interest], those are the companions of the Fire; they will abide eternally therein." (Quran 2:275)