First of all, it is a protection against the double spent. There was some time interval of two parralel blockchain for this coin and coins spent in one branch remained unspent in the other one. This does not apply to coins sent to an exchange, those coins were spent and there is no easy way how to censor them. You surely will lost your coins if you were one of the attackers. If you only bought coins on Jubi, I do not know, if they were the coins from attackers or from other earlier miners. Because Jubi runs on an old version of wallet, I recommend to do the withdrawal from Jubi into the old wallet, then make a backup and try to upgrade to the new wallet version. If your coins survive, then they were valid and can be used.