Clutch stiffening

Slm friends. In recent days, the shifting of the gear has gotten heavier and the clutch pedal has gotten pretty hard. Where could the problem originate? My car 307 1.4 HDI 2004

I have the circulation rope and / or transmission oil checked.

I don't know why, but when I changed the pad and balls, it softened as if there was no clutch, I got used to it in 2-3 days. The pad was very worn out of me.

I just replaced transmission oil with engine oil.

The clutch hardness is something I don't like, though I got used to it, but I would like my friend to be as soft as his 2013 Partner. But I guess in ours there was no rope in the clutch, the master said so. So we couldn't soften or get that extra space in all the 307s below.