Your post are misleading. It sounds like they did not fill the system and yet you had pressure and then they filled the system. So did they really fill the system?

1) you need good air flow across the evaporator coil (the one inside and makes the car cool). Have you check the air filter for the AC?

2) When you took the system apart did you allow it to completely dump? Or did you shut it down right away?

3) Most Car ACs has two pressure switches. The High Pressure acts as a safety. The low pressure is what controls the compressor. The liquid freon goes to the expansion valve or orifice as it expands it takes heat out of the evaporator. Meanwhile the compressor is sucking and compressing the gas. If there is not enough heat to expand the liquid into gas then the low pressure cuts off the compressor until there is gas to compress.

So that means until pressure goes up, then compressor will not run.

4) Buy a AC gauge kit. Well worth it to have. You should be able to see low pressure side changing up/down to cause the compressor the cycle.

5) If you compressor is running however it's not cooling then you might have an airflow issue OR a bad low pressure switch stuck on.