Car still losing coolant after head gasket replaced

I drive a 2004 polo and have only serviced my car at autoworks milnerton. And the service has been good but there were a couple of issues. Let's start with the first, spark plugs leads replaced 3 times in 4 years. Everytime my car went for a service I drove it away there was slight hesitation and was told to replace my spark leads, apparently a polo problem. The 3rd time it happened the previous plug leads were out of warranty by two weeks, the quote for the new brand replacement leads were 1800, they were probably some special leads and I wasn't happy and autoworks replaced it for free. Before the 3rd plug lead was replaced my car was using coolant and it overheated. The thermostat was replaced. It leaked and took it back they replaced a circlip and it wasn't leaking. Car was still loosing coolant and I was really worried that it would be an expensive head gasket job. So I took the car for its annual service and thought maybe the expansion tank was busted because it made a booking noise after driving, paid just over 3600 and the car over heated again and went back the next day. My worse fears were confirmed it was head gasket paid 7000 and warrant paid 2500. Now I was very cautious checking the water level and it still dropped. I topped it up to just below max while the car was cold thinking maybe because of the heat and 2 weeks later the coolant level drops below minimum. Sent an email with 2 pics showing the coolant level about 3 days ago, got a reply to say it is with a technician. Now I have replaced at autoworks, my water pump about 20k kms ago, thermostat was replaced twice, once when it overheated and 2nd time it was replaced when a new head gasket was installed and a new expansion tank but the car is still using coolant. Over the 4 years I must have spent closer to R40k at Autoworks which is probably what my car is worth because I want my car to be in good condition but the latest where I have spent 7000k for a head gasket job, autoworks got paid a total of 9500 and over 2k for service, it was 3600 but I am excluding the new bottle as it wasn't the problem and with all the other things replaced like thermostat, waterpump and still my car losses coolant, I am at a loss as what more can be done. The car does not lose coolant rapidly but over a period of time and I did take my car in for 1000km check but at that time it also went in to check why the car was hesitating and that was were the plug leads were replaced. I take really good care of my car and I put all my trust in autoworks. It is a really dissapointing that I still have the same problem that 7k should have resolved