It's your responsibility, not the custodians responsibility, to track you basis in Roth IRA contributions because a particular Roth IRA custodian has no way of knowing how much Roth IRA contribution basis you might have acquired by making Roth IRA contributions at other custodians.
As fanfare mentioned, your Roth IRA contributions are reported to you and to the IRS on Forms 5498. The accumulation of your Forms 5498 reporting contributions which add to basis, Forms 1099-R reporting past Roth IRA distributions which reduce basis, and your Roth IRA account statements are what document your basis in Roth IRAs.
