Re: Is this true?
When you ask your Mum for help, the schoalrs have said this is help from a person who is able so it is allowed as attested by the Sunnah.
When you call upon the dead, they are unable, resting in the Barzakh seeing their place in Hell or Heaven day and night, and cannot avail you.
Thus, making a false Qiyaas, as the Braielly do, of the living for the dead is what leads one to make istigathaa permissible when in reality it is not.