I referred to the profile you created in the website and see that you have no model number listed of your refrigerator. I will only be able to give you basic information and things to check.
Freon never goes bad. Freon may need to be added once a technician diagnosis it to be low due to a leak. The leak would have to be located and repaired before freon can be added.
There could be several reasons causing your refrigerator to not achieve the same temp as before.
Dirty condenser coils
Failed condenser fan
Failed evaporator fan
Freon leak (low on freon)
Not knowing what type refrigerator you have, the condenser coils may be under the refrigerator or on back. If the condenser coils are on the back it will not have a condenser fan motor. If the condenser coils are under the refrigerator, unplug the refrigerator and clean the condenser coils with a brush or vacuum. The vent grill should pull off to gain access to the condenser coils under the refrigerator.