Did you mean to say that at your Supercharger stop that unbeknownst to you, your charging session never started because of some kind of payment method issue, and that’s the reason the idle fees were charged?

Not that you plugged in, did get at least some charge, but your charge limit was reached, and then you started to accumulate idle fees that you thought you were immune to because of your lifetime free Supercharging?

Of maybe it wasn’t even a payment method problem at all, but someone your charge limit got lowered to a very low percentage during your service visit and you didn’t realize it so that when you visited the Supercharger you were already above (or at least very close to) that charge limit?

Finally yes, it’s certainly hard to contact Tesla (or any large company these days) by phone, but I do suggest you reach out via their preferred methods…I have heard of people just recently getting a one-time waiver of idle fees due to a misunderstanding of how they work.