Hello Binita,
How old is your son? How much does he weigh? Also, what is his ferritin level?
There is a good chance that the toxicity has cleared out of his system by now, but you should definitely have that confirmed through a hearing test.
I don't think that you have much to worry about about at a young age, if he has been well chelated for many years in terms of iron accumulating in his other organs so quickly.
When you restart him on chelation, start on a low dose and split that dose so that he's taking it twice daily. Slowly increase it to the therapeutic level and he should be fine.
My son had a similar effect with desferal when he was 5 or 6 years old. We withdrew desferal until his hearing test came back normal and then restarted. This is fairly normal in young children.
Best wishes to your little man
Sharmin