You can take the medical insurance card to any pharmacy, draw it and you can see the balance, or you can log on to the social labor security network of the Corps to inquire. If you can't find it, you can also take the medical insurance card to the personal account department of the medical insurance center and ask the staff to check it for you.

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