--increment-min and --increment-max are command line arguments that can be used in a mask attack (-a 3. Well, it is also supported in -a 6 and -a 7 actually, but always together with masks).
if you use --increment-min and/or --increment-max you also need to specify the --increment command line flag.
an example would be
Code:
hashcat -m 0 -a 3 -w 3 --increment --increment-min 4 --increment-max 7 -2 ?l?d hashes.txt ?2?2?2?2?2?2?2?2?2
Note: the mask itself, in this case ?2?2?2?2?2?2?2?2?2 which was defined in this example to use all lowercase letters and digits, must be *at least* as long as --increment-max, but can be longer
... and no, there is no bullet-proof way to say "this is how you 100% crack all of these hashes", but you might research what are the best ways to target a specific hash lists which was discussed a lot of times within this forum (and in several external blog posts etc). In general, a small but very targetted and well-working (non-crap, overblown) dictionary together with special and/or well-known/good rules is a good start.
On the other hand, if you say that you have a lot of hashes but crack none of them (it wasn't clear from your description above), then you indeed might be doing something wrong or there is a very special password policy (but in my experience one does also crack several hashes - the low hanging fruits - even if the password policy is very restrictive given that the hash list comprises a lot of hashes, at least some thousands).
