After making a bunch of new decks on anki the computer app, I finished and closed everything. Then later I wanted to do them on my phone app version of anki but they werent showing up, so i pressed sync. It usually prompts me to upload or download but it didn’t this time. So i went to ankiweb on my browser to check and it had overwritten with the old one from a few days ago instead. No its not my first time pressing sync, i already had a deck i created on the computer app that i had successfully downloaded. It just didnt prompt me and now all my cards have gone. 
i did not export the cards or anything or idk if theres a way to make a backup before risking syncing with the phone app. I had pressed the sync button on the computer app and it seemed fine i dont know what happened.
Hi, i forgot to mention but the laptop i used was a borrowed laptop from my university so i dont have any local backup files because i have no idea whoch laptop i was using.
I have made cards on a borrowed laptop before and it synced properly with my app on the phone, all i did was press download from ankiweb. It just didnt prompt me this time and synced my phone app to anki web so i lost several decks.
So i went back to borrow the same laptop and luckily i guessed which one it was correctly and was able to access the backup since nobody had logged in and wiped the local drive. I just logged in and synced it then downloaded ankiweb onto my phone and it prompted me this time.
That’s great! It sounds like you’re all restored then?
You can work on your collection on a borrowed device, but make sure that before you do anything else, you set up syncing with AnkiWeb and download your collection. If you create a new collection on that device instead, then you’ll have to merge the collections together before you can sync successfully. Syncing with AnkiWeb - Anki Manual
Syncing when you open the app and when you close/leave the app, on every device, every time, is the best way to avoid syncing conflicts that create unrecoverable situations.
I synced on the borrowed laptop before closing it down, the issue arose when i tried to download my save from ankiweb onto the ankidroid app, i pressed the sync button but it didnt prompt me to download, it just uploaded what was on the app onto ankiweb. I synced successfully before though. I dont know what caused the issue. But thanks for the information regardless.
It may be useful for you.