Hey there Friendlyfishies :)
The great, and sometimes most frustrating, thing about bettas is that they're all individuals. They each have their own little personalities and quirks and preferences.....and some are a little pickier and take a little more time to settle into their new homes and eat then others. ;)
How many days have you had him exactly? It can take two weeks for your betta to get used to things and start eating his pellets, especially if he wasn't fed pellets before(I always have trouble with fish my local Petco, who I'm positive feeds mostly bloodworms).
What pellet brands have you tried? I find the more fussy bettas tend to reject the not so great brands like Tetra or Warldeys. Have you tried Omega One or New Life Spectrum? Those are the two best brands, most fish should go for them.
Are the pellets possibly too large for him? You can try crushing them up and see if he eats them then.
Another option to make the pellets a little more enticing is soaking them in fresh garlic juice. I've never had to do this personally, but I've heard its a great way to get a picky betta interested in his pellets.
Also, I would advise you ditch the freeze-dried foods all together....from what I understand, they have very little to no nutritional value and they have a history of causing SBD/bloating problems. Instead, to add a little variety a couple of times a week, pick up some frozen bloodworms and/or brine shrimp.
Flakes really aren't the best of foods either....its difficult to dole out a proper amount and they can become rather messy....but so long as your fishes staple diet is a good pellet brand, the flakes are made for bettas, and you're careful when feeding them then you can use them to add a little variety if you like.
The important thing when trying to get your betta used to pellets is to stay strong, remember you're not starving him(he can go up to three weeks without food), and keep offering him nothing else but the pellets until he eats them. He will eventually. ;) Good luck!