Antisocial Guinea Pigs That Won't Eat Fruits or Veggies?

I have 2 male guinea pigs that aren't a year old yet, they refuse to eat fruits and veggies that I give them as they don't see that its food so I have to give them yogourt drops with vitamin c in them which they eat. (their for guinea pigs and I get them from the petstore). They refuse to eat good things for them, but yet they have no problem chewing on the cage, and plastic in the cage, and the bedding I have them in. (a mix of fleece and paper pulp). Does anyone have any ideas on how I can get them to eat fruit and veggies, i have tried so much, even placing food in their mouth only to have them spit it out then sc their tongue off on their teeth (really cute but not helpful). I'd love any help that anyone can offer. Thanks so much!