Rav Dovid Feinstein shlit”a’s holding in the name of his father that it is mutar even when cy is readily available is not in the Igros either.
And you keep asking for a source for the story, but what difference does it make? It’s not in the Igros.
Also, where in Igros does it say that something which is not in the Igros is wrong?
And if you think that teshuvah is wrong, why did he write it?