cannot reach apex

Hello everyone, Sometimes, as in this case, I struggle to reach the apex.

The tooth in question is a necrotic lower first molar. As seen in the X-ray, I can't reach the apex of the mesial root—I get stuck at roughly the same point in both the buccal and lingual canals.

Could I be blocked at the junction of the two canals?

I tried instrumenting with a 25 rotary file about 1-2 mm short of the working length and then attempted to find an opening with a size 8 K-file(always precurved), but no luck.

Any advice? thanks to everyone