Default [Q]Problems writing on internal storage

Hello! after looking for a good week or so and havent found anything similar i thought i might ask about my issue

i bought two phones a while back and while one has been flawless and basically unbreakable(my dad loves dropping phones, its amazing it hasnt shattered or somerthing) its a whole other history with mine, from day one ive been having issues with the sd card, by today it has corrupted 3 sd cards, i just stopped using external storage

but now my problem is that it has been acting strangely with the internal storage, making backups on titanium and disappearing, whatsapp backup is a month old, but supposedly it runs each day, and today after flashing a custom rom(Carbon, that ive flashed before) all my data disappeared and the sd is as if it was formated, and on the Disk Usage app i have a huge 6.5gb file named as "system data" that is nowhere the MTP connection doesnt works either

for more info, ive tried full stock roms(V20j), Carbon(that works usually until today's issue) and a few others, all of them have the same issues with writing, has anyone come across this kind of issue before? any help would be greatly appreciated!