SMCKIE1993

It is a TDI 1.6 Diesel (Automatic Gearbox)

I am looking for some assistance in regards to my car coolant issue. Recently I had a coolant leak into my passenger side of my car and had to get a new heater matrix installed. When I collected the car the person who done the repair told me to keep an eye on the coolant level for next couple of days as he hoped to be able get more coolant as he reckons he managed to get 3l in, got car back on Tuesday. I had check my levels on the Wednesday and Thursday mornings they seemed to be fine, however, on Thursday night I went out to get some shopping and my check coolant light went back on and the tank was empty when I pulled over to check. My coolant temperature gauge went over the 90 mark but did not head into the red. Got my car towed back to the garage who checked it the next day and the mechanic was honest and told me that he didn't fully connect the hose that connected to radiator properly after he drained the car of coolant during the matrix fitting. He rectified the problem and filled the car up with more coolant and dropped it off at my work, which is only a minute away for the garage. When I finished 4 hours after receiving the keys I got into my car turned the engine everything was fine until just after taking off my coolant light came back on, check the coolant tank and it was empty again. There no signs of leak in passenger footwell and smoke either. Like the car worked fine when I got it back from matrix repair on Tuesday, Wednesday and Thursday morning even driven it 100 miles on Wednesday. So I am completely baffled, I have left my car with the mechanic to check over on Monday but I am hoping the isn't anything serious. Does anyone know what might be the issue here?