If your balance exceeded £25,000 before the migration to the new issue 3 product in January 2016, your entire balance will have been migrated.
You will no longer be able to make deposits into your Save to Buy Issue 3, unless you take the balance below the account limit. You can make one withdrawal per account year without your interest rate changing. Further withdrawals are allowed, but your rate will reduce from the date of the second withdrawal until the end of that account year.