Update:
I managed to use successfully micro SD card adapter and ENC28J60 with STM32F103C8 but Ethernet module was freezing after using the SD and the loop() wasn´t cycling, after several attempts and doing changes on software and hardware I finally acheived it by following these tips of SPI bus: (Better SPI Bus Design in 3 Steps)
Note: Sometimes the ENC28J60 hangs after some time (e.g. after a GET request) and a hardware reset of the module is needed.