EV points aren't gained according to level, they are gained according to items used/ battles won.
When you battle a wild Pokemon, you gain the EV(s) after you've defeated the wild Pokemon.
When you use an EV increasing/ decreasing item on your pet, it will take effect immediately.
If you have not been keeping track of the wild Pokemon your Excadrill has battled, then it's probably used up its 510 EV quota, which means that it cannot gain any more EVs in any stat.
Additionally, a Pokemon will only take 100 EVs from Vitamins (so 10 vitamins) in one stat, and then it will reject them afterwards. Also, it will only accept the vitamins for its first 100 EVs in the specific stat, so if you already have some speed EVs then it won't accept the full 10 vitamins.
Berry EVs removed
Pomeg Berry -10 HP EVs
Kelpsy Berry -10 Attack EVs
Qualot Berry -10 Defense EVs
Hondew Berry -10 Sp. Atk EVs
Grepa Berry -10 Sp. Def EVs
Tamato Berry -10 Speed EVs
These are a list of EV reducing berries, and if you give 11 of each berry to your Pokemon, it will have 0 EVs, which means you can EV train from the beginning.
11 berries are needed because the first berry reduces the EV in a stat to 100, and the other 10 take away that 100.
Marriland's EV guide
Serebii's daily events list (where the EV berry seller is listed)