INCREDIBLE MISHAP!

I got an HP laptop from the Clearwater store and it started giving me issues along the way so because I moved the Cresta branch is closer. I took my laptop to be fixed there they told me it would take about 3 weeks. I explained to the tech guy that the laptop keeps flickering everytime I type especially when using excel, the screen goes blank and the laptop keeps making beeping noises. The guy that assisted me said it could be the graphics card or something. I initially thought it had something to do with the screen or something internally that might be faulty. I waited over 3 weeks to collect my laptop and I asked what was wrong and the guy said it had to do with the battery I was surprised because the battery was fine but then because I'm not an expert I just took the item and headed home. To my surprise the laptop was still doing the same thing and now worse my battery is used up even quicker than before. I called in the same day to notify them of this matter it took hours to get through cause apparently their line has an issue. I was asked to bring my laptop in and that the matter would be escalated. I'm super disappointed because firstly I feel the technicians need to bare in mind the issues the customers bring forward and check that before assuming their own opinions of what could be wrong. They assumed the battery was the cause and changed the battery now the machine is worse. I have no words because I work from home and require the laptop do so. I'm just disappointed and frustrated cause now I have to wait another 3 weeks + for them to sort this out. This is unacceptable how do they misdiagnose an issue like this?