Repair specials/ but phone keeps breaking since repairs done

I have never been so frustrated or irretated by so called repair spesialist. They advise they can fix they phone, but since repair the phone has never been working properly. Why advise you can fix something but cant. I was adviced that their is a one year warrantee on the repairs. But when i took the phone back they advised me its only 3 months. Why would anyone fix a phone and pay so much money if the phone will only last 3months. I never had ones day problems with the phone untill it went to we fix, i wanted the battery replaced as the batterys life was to short. They replaced the battery but had issues with the phone screen keep on going blank and rebooting , took back in and after a long argument they replaced the battery. Know yet again it is doing the excact same thing. Its so frustrating as you because you wanted a better battery life. Why do they say they can repair if it keeps on breaking. I never had this issue before. I had insurance on the phone, and the insurance would of replaced the phone. Since i cancelled my insurance and know yet again im sitting without a phone as we fix never advised id have any issues with replacing the battery.