A/C stopped working

Hello, my A/C has stopped working completely now. It was working partially before, then it almost ran out of Freon so I had a car shop add Freon with dye and they said they would tell me if there is a leak I went back three weeks later for them to check leak. They said The Freon was gone again already and they said we can’t find the leak and asked me to pay more money to refill and try again and I said no. Very disappointing. My A/C worked partially before going there and now it doesn’t at all. When I say it worked partially it’s because yes my A/C did work before going there but only if I kept it on a certain “direction” the -on your face and feet, but cold air would only come out of face part. I originally had began to learn how to work my car A/C and noticed if I moved the air blowing direction knob the A/C would stop working- but only for two days and if I moved it back to the correct direction and did not touch it for two days then it would start working again, after the two days of no use. Also, my A/C has always made weird sounds. Even while off. Like it rumbles. Especially when I first turn car on. What to do now? Thank you!