Can't reinstall nothing to /system

I tried to update my Xiaomi Mi A2 to Android Pie since yesterday the Beta was Released. At first, I tried to install the official provided one, but after facing some errors, I installed the Treble version of the Android Pie Pixel Experience ROM. It was working perfectly, but after installing Pixelify with Magisk, my WiFi stopped working, and I got the error MAC 02:00:00:00:00. After trying some things with terminal apps and root, I opted for reinstalling the modem image, which I thought that could solve the problem, but instead, the phone didn't turn on, it kept on the Android One screen. So after waiting for some hours, I decided to format the phone and lose all of my data. I formatted the system partition with fastboot erase system_a and fastboot erase system_b, but when trying to reinstall the PixelExperienceP ROM, I receive this error again and again: fastboot flash system_a PixelExperienceP-arm64-ab.img Sending sparse 'system_a' 1/5 (524284 KB) FAILED (Error reading sparse file) Finished. Total time: 24.591s After that, I am not allowed to send any command to the phone until I restart de bootloader. I have tried to install different ROMs, the stock one, other Android versions, but I get the same error on all of them. Please, any ideas on how to solve my problem? I am really worried about having broken it. Thanks in advance.