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Very well done. And the ducks -- hilarious! Now how do you scale and vary this enough, to prevent suspicion? That's the next step. Near the end (28 min), it felt like the caller was probing with "can you hear me" to collect Lenny's canned responses. Would it be better to hang up earlier to avoid suspicion?
"Lenny" is only 21 short recordings, stitched together into a crude sequence. It's a remarkably unsophisticated trick on a technical level. It wouldn't be difficult to produce dozens or hundreds of Lennies on quite a small budget. Tweak the script a bit, get someone on Fiverr to record it and you've got a new and unrecognisable Lenny MkII.
I'd love to see it as an app with a blacklist for spam numbers or telemarketers. Use a better text generation engine like a modern deep learning based generative model, and deep voice or crowd-sourced recordings.