your break statement should break out of the for (in in 1:n).
Personally I am always wary with break statements and double check it by printing to the console to double check that I am in fact breaking out of the right loop. So before you test add the following statement, which will let you know if you break before it reaches the end. However, I have no idea how you are handling the variable n so I don't know if it would be helpful to you. Make a n some test value where you know before hand if it is supposed to break out or not before reaching n.
for (in in 1:n)
{
if (in == n) #add this statement
{
"sorry but the loop did not break"
}
id_novo <- new_table_df$ID[in]
if(id_velho==id_novo)
{
break
}
else if(in == n)
{
sold_df <- rbind(sold_df,old_table_df[out,])
}
}