Hi there! I am a Lenovo user. My phone's internal storage is 16 gb and external SD card is of 32 gb. All of a sudden,my SD card failed to save or download any media. So I formatted the SD card. I even rebooted my phone. I set everything and started using. However the same issue occurred with my SD card failing and showing a message that says "SD card full or unavailable" although there's about 25 gb space left on the card. So I changed the storage option on my phone from external SD card to internal storage an it works fine. However 16 gb internal only is not sufficient for my usage. Is the problem with my phone or the SD card? Please help me know