The 33-year-old was charged with failing to report an incident of alleged match-fixing during a Serie A match between Bologna and Bari in 2010.
The resulting ban has seen him confined to the sidelines as the Rossoblu continue to struggle in the lower reaches of the league table and he revealed his anger.
Ahead of his return to contention at Napoli, he told La Repubblica: "The worst part was being associated with something I never did.
"But I've tried to make the most of this situation and take the positives from it. I've spent time with my family and learned to appreciate my true friends.
"I don't think I have made (any mistakes). I faced the situation without fear. Only this morning, though, I heard someone on the radio say that I've sold games, and that hurts.
"But I am made of armour and I want to fight for this shirt. I will always remember it as a bad time but, sometimes in life, testing scenarios have to be encountered head on."
The Italian Football Federation's (FIGC) wide-reaching investigation also saw Juventus head coach Antonio Conte banned from the game for 10 months, with his suspension subsequently reduced to four months on appeal.
Portanova added: "I know him and I understand (what he's been through). I never believed anything that I read and I was been in the middle of it too so I was even more convinced.
"I'm happy for him and for myself and I don't want to talk any more about this unfortunate episode. I hope you will only ask me about what I can do for Bologna."
Former Bari defender Andrea Masiello, who originally implicated Portanova, was handed a 22-month suspended prison sentence for admitting scoring a deliberate own-goal in a relegation decider against Lecce.