Well, the pins don't look damaged at least from what I can tell from the second photo, so we can assume the save data itself is corrupt.
You have two routes to try if that's the case:
A: On the title screen, press Up on the D-pad, Select, and B buttons simultaneously. This should bring up a prompt to delete all save data.
B: If you have a hacked 3DS, you can use savefile manager homebrew software such as JKSM, Checkpoint, etc. to wipe it manually.
If either of those options work, then you should be able to start a new savefile and play it. If not, the pins may be damaged even if they appear fine and you've cleaned them. It may also be an issue with the DS, so you can try using compressed air to blow out any dust in the cart slot, (and please use a can of compressed air or air compressor, NOT your own breath. Water-vapor on your breath can cause water damage, blowing into your cart slot/into the cart can damage it more).
You could also try applying a thin layer of tape or something else to the front of the cart so that the pins on the cart are wedged more firmly against the contacts in your DS.
If none of the above solves the issue, the cart is likely damaged internally, and there's not much information available on how to diagnose and repair the issue.