Bricked Lenovo Vibe shot z90-7, no edl, fastboot twrp and locked bootloader.

I got a lenovo vibe shot z90-7 which was using Android 5.1. I found an upgrade rom on needrom to 6.0. I flashed it using qfil (qualcomm flashing tool) and it went all right, all functional. But I also wanted to unlock the bootloader and install a twrp (I found a procedure and twrp image on a russian forum). I followed the steps but it didn't work, I still wasn't able to unlock the bootloader. Thus, I was not able to enter fastboot anymore: from adb I was typing "adb reboot bootloader" and the device would reboot normally, not in fastboot mode. I decided to change to another rom (from needrom) which was claiming would allow you to unlock the bootloader. So, without hesitation I flashed it in qfil (edl mode) and it went all right, but I got stuck in boot loop. After the splash screen, the device shuts the screen off and does a long vibration and stays like that. If I connect it via usb to my pc I get a some "need to format drive" alerts, and in qfil I see "Qualcomm HS-USB Diagnostic 9006 (COM5)". If then I try to flash the rom I get this log:

Code:

---

Start Download
COM Port number:5
Switch To EDL
Download Fail:System.Exception: Failed to Switch to Emergency Download mode

  at QC.QMSLPhone.Phone.QPHONEMS_SwitchToEDL()

  at QC.SwDownloadDLL.SwDownload.SwitchToEDL()
Download Fail:Switch To EDL FailSystem.Exception: FireHose Fail

  at QC.SwDownloadDLL.SwDownload.SwitchToEDL()

  at QFIL.Tech.DownloadTech.SwitchToEDL()
Finish Download

---

It's seems like I need to get in Edl mode first, but I cannot use adb and pushing vol+ and plug the usb at the same time (or a little bit first one or the other, I tried all) does't do anything but booting the device normally.
I also tried getting in fastboot mode (keep vol- and power button) but it doesn't work.
I read of an "engineering mode" by keeping vol- on boot. It does something, the screen becomes black, but it's on. On my pc the adb driver comes in in the popup, like if I'm in fastboot or adb, but on "fastboot devices" I can't see anything, while on "adb devices" I see a device, which is "? unauthorized". Strange to me, I can't do much with it since it's unauthorized and the screen on the device remains black. And after a few seconds (about 30) it gets back to long vibration and screen off state.
I can get into the stock recovery by holding vol+, vol- and power, but it's a very poor recovery. All I can do is reboot, shut down, wipe data and update. I tried to use "update" and put a zip file of an official rom downloaded into the sd card and named "update.zip" as suggested by the recovery, but I get an error (with no technical information about what kind of error), so no luck with that either.
I tried to force the qualcomm driver from "Qualcomm HS-USB Diagnostic 9006 (COM5)" to "Qualcomm HS-USB QDLoader 9008 (COM5)", then tried to flash using qfil, but I still get an error, even if this time is different:

Code:

---

COM Port number:5
Sahara Connecting ...
Sahara Version:0
Start Sending Programmer
Download Fail:System.Exception: Unable to download Flash Programmer using Sahara Protocol

  at QC.QMSLPhone.Phone.QPHONEMS_SaharaArmPrgDownload(String sFileName)

  at QC.SwDownloadDLL.SwDownload.QPHONEMSSaharaDownloadArmPrg(UInt64& version, String armPrgPath)
Download Fail:Sahara FailSahara Fail
Finish Download

---

I finally tried to download the rom in .qsb format and get in engineering mode again, but the screen remains black and no sign of flashing possibilities.
Please help, I tried everything it came to my mind.
I also tried with miflash, but still got errors...
Thank you

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