On the planet the general flow of the mission is as follows:
1. speak to ferengi
2. speak to miners and if tactical kill 4 groups of thugs, 3 in the grounds and 1 just outside the city
3. speak to ferengi
4. enter mine
5. kill guard as he isnt worth the effort to talk to (I do this on kdf a lot)
6. kill groups of romulans in cavern:
1st group (3) to left of cavern entrance
2nd group (3) to right of cavern entrance
3 rd group (3) by stanchion in middle of cavern
4th group (2) by desk back right of cavern
5th group (2) at back of cavern opposite where you enter the cavern
7. then examine campsite
8. open secret door using panels
10. kill romulan spies (again i play on kdf a lot so it just fits)
11. enter command room, free prisoners and kill commander for key
12. use key, then enter corridor and kill 2 groups of romulans
13. cutscene then download data
14 escape mine, possibly with a detour to kill any remaining romulan personnel and get horta accolade
15 speak to ferengi
16 beam upto ship and examine/decrypt data
when entering the main part of the cavern it is possible you drew aggro from too many squads at once and somehow managed to lose a romulan so you couldnt kill all the groups. These groups are best being lured to you so they dont get reinforced by allies.
Hope this helps so you can more pinpoint where you have issues.
I'm in the mine itself, killed the first guy and then as you move into the first large cavern there were three groups of Romulans with no fourth group anywhere in the areas available and no way to advance further into the mine map area.