You happen to be forgetting the final paragraph of Animal Growth, which states that multiple magical effects that increase size do not stack. This means that when Animal Growth wears off, its effects do, too, as well as only getting a single size change between the two spells. And then CFH's effects take over, and since it mentions no changes to stats due to size, RAW would state that you stay with the original scores. However, I believe by RAI, you can still adjust things according to the size change chart in MM, page 291. A small creature changing to medium, for instance, grants +4 str, -2 dex, +2 con, and -1 to the size bonus to attack and AC. Now, take the standard dog from the MM, apply the creature size changes, and for ability scores you're looking at 17 str, 15 dex, 17 con, 3d6 int, 12 wis, 6+1d3 cha.