Is the third-party company also a third party to pay social security and wages?

It is also a third party. The head office entrusts the payment of wages and social security to the third-party company through the personnel agency service contract, and the third-party company remits the above expenses to the third-party company and pays wages and social security to the workers in its own name. The head office only entrusts the payment of employees' wages and social security to a third party, rather than labor dispatch in the legal sense.