Will the social security I bought while working in Shenzhen be cancelled if I haven't paid it for many years?

Social security is linked to the ID card, which means that an ID card number will only have one social security account number and will not be cancelled, but it will stop after you stop paying. If the new company has social security benefits after job-hopping, it can be renewed.

Social security actually includes a number of insurances, among which endowment insurance can be accumulated. For example, you paid social security in Shenzhen for five years, and then stopped for many years. Then, after you stop paying, all other insurance items in your social security have stopped and the expenses have been cleared, but the endowment insurance will accumulate, which means that your endowment insurance has been in existence for five years. In other words, at present, the national policy endowment insurance can only be paid after 15 years. Then with the follow-up insurance, you only need to continue to pay 10 years to receive the pension.

Further reading: How to buy insurance, which is good, and teach you how to avoid these "pits" of insurance.