I have an RO system for drinking/ice cubes. I changed all the 4 filters 3 months ago and all of a sudden it stopped working. I was told I needed a new storage tank (3gal). MI replaced the tank and still no water. The filter is making water but its not filling the tank.

Bunch of questions before we start. How long after the filter change did the filter stop. Who told you a new tank was needed and what reason or evidence did they rely on to make that judgement? You said"The filter is making water but its not filling the tank" what evdience doi you have o this? Back to you

It takes about 24 hours before you get first cup of filtrated water.

It appears your system is not connected correctly or you forgot to open one of the many valves in the system.

Are you sure that your membrane was sized for that system? It could be that all of the water is going to drain due to incorrect sizing. Or, you could received a bad membrane. If the membrane was on a supplier's shelf too long, it may have become defective.
Or, it could be that you do not have enough water pressure to force the water through.