All perfect praise be to Allah the Lord of the Worlds. May His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
Caring for the citizens is the duty of the state, but in accordance with its potentials. Social security is part of performing this duty since this system is responsible for helping the older persons in need, who meet the laid down conditions. Some of these conditions are:
Paying contributions in advance or later and these are framed as donations paid by citizens to the Social Security Fund, which guarantees that the state performs the duty of care towards its citizens.
Therefore, the Administration of the Social Security isn`t sinful for laying down detailed terms and conditions showing the amounts to be donated by the participants and whoever wants his previous contributions to be taken into account, whether these amounts were more than his previous contributions or equal to them. This excess amount isn`t considered forbidden usury (Riba), because usury is a conditional increase in a commutative contract or a loan while the money paid by social security participants or one who has renewed his participation is a donation, not a loan nor a commutative contract.
In conclusion, a participant who wants to change from the new system to the old isn`t sinful for repaying contributions of previous years of participation in the social security, even if they were more than those previous contributions. And Allah the Almighty knows best.