I think you might have lost it (the variegation) variegated trees and shrubs often do revert and because the all green reversion is stronger than the variegated shoots, the green ones gradually take over. To prevent it you have to be vigilant and cut off EVERY green bit as it appears. This can happen even on ungrafted specimens but additionally on a grafted plant, the host plant can start to shoot, again it will be stronger than the grafted top and it will take over entirely.
So....is your plant grafted or ungrafted? If its grafted and its now all green then you are stuck with what you have. If its ungrafted and all green, you might save the variegation by cutting off EVERY BIT of the green shoots. Hopefully it will shoot again and hopefully the shoots will be variegated. The risk is that this huge pruning might kill the plant, also it might just regrow green again. Your choice.