Vauxhall ADAM battery keeps going flat

My car keeps going flat. I’ve taken it to the garage and they said when the car was put through the diagnostics it lit up but nothing was actually wrong! Didn’t look like a battery issue but overnight the battery drained so they assumed it was the battery and gave me a new one (also they said a fuse was blown and they changed that for me too).After a few weeks same issue came back, car going completely flat but I have no warnings or anything like that on my dashboard. Took it back to the garage and they couldn’t figure it out, they said they ran tests to see if I had a parasitic drain and they checked the voltages and alternator but all looked normal, they gave me the car back and had charged the battery back up! But the car is back to going flat all the time,it’s now at the point it’s dead everytime I go to drive it!

Any help on figuring out the problem would be amazing! Thank you in advance 🙂 (I have tried to get booked in with a vauxhall specialist garage but all in my area/2hr drive away have their books closed right now due to being too busy)