Hello,
What do you mean exactly by stopped responding? Is it permanent?
There is no reset to factory function.
But, the I2C address of the ST25DV04KC is configurable. The default address 0xA6/0xAE but this can be changed by writing the I2C_CFG configuration Byte at system address 0x000E.
You may have accidentally overwritten this default value with something else. If this is the case, your ST25DV04KC now has a different I2C address. You can check in your code if you make any write to address 0x000E, and check the value you wrote to recover your new I2C address. If you can't find this in your code, then you will have to "scan" for the 128 possible codes to find at what address the St25DV04KC is answering.
Best regards.