Is it permissible to pay fictitious social security contributions in the name of another establishment in order to obtain a suitable retirement pension after the request to return to the previous job was denied?

You are not permitted to engage in the aforementioned stratagem, nor is it permissible to voluntarily subscribe to an insurance fund based on gharar (excessive uncertainty) and qimar (gambling). If you are coerced into it, or if you subscribed to it unknowingly of its prohibition, then you may not benefit from it beyond the amount you have paid. Your action involves deception and trickery, so fear Allah and seek lawful means. Invest your money in a permissible project that will suffice you from the unlawful, for whoever fears Allah, He will suffice him and provide for him from where he does not expect, as Allah Almighty says: "And whoever fears Allah – He will make for him a way out And will provide for him from where he does not expect. And whoever relies upon Allah – then He is sufficient for him. Indeed, Allah will accomplish His purpose. Allah has already set for everything a [decreed] extent." And remember that no soul will die until it completes its term and its provision. So, fear Allah and be moderate in seeking sustenance, and let none of you seek provision through disobedience to Allah, for what is with Allah cannot be attained except through obedience to Him.