Unhappy [Q] OTA update from xpeia sl

I have xperia SL version 4.0.4. Actually, it used to be 4.1.2 but I flashed it to MIUI then I flashed it back to firmware 4.0.4 (becasue of some problems found while using MIUI) because I could not find the firmware 4.1.2. Luckily, I got OAT update of version 4.1.2 LT26ii_6.2.B.0.200. When I completed download the update, and press install update, my phone turned off and then it turned on again with the message: could not install update. I tried download that again but the same thing happened. I tried to use Sony pc companion to update through computer. Yes, it has found the latest update for it 4.1.2 LT26ii_6.2.B.1.96. But I dont know why? while I am downloading the update, it never completes. when it is nearly 100 percent then it started to download again with like 0 percentage. I also tried that twice, the same thing happened, Why?
Btw, I am new to the website and I know very little about android. thank in advance!