If the person I filed with direct depostited my return into her account how can I change that?

The tax preparer I filed with this yr had my check direct deposited into there account. Can they do that without my authorization. Another question is when the irs send rebate checks out in May how can I change that to ensure that this check does not also go direct deposited into their account because I dont want any more confusion with this company then they already have given me? Thank you for your answers or advice.