No, you can't get back test net coins to main net. If you are wondering that's possible then you are wrong. I think you already got your answer from here especially from Heisenberg_Hunter explanation. I am assuming someone trying to make you fool or you got scam (if you paid someone for test net coins). Your testnet balance can't use anywhere, isn't sound like just for "test"? However, as other already said, it would be more better to explain you if you expose whole story how you have got that coins.