When you said "the provider is apparently billing me for $450 plus interest for both the incorrect out of network deductible $300 and correct in network deductible $150", did you mean that's what they were incorrectly billing you BEFORE and the corrected amount due is $114.94?
In any event, if your calculations are correct and you are indeed owed the $80 and change, sending a certified letter to the company you paid the $195 to with the corrected EOBs, demanding a refund of the overpayment should get things started. They will likely refuse or not respond. It would then be your choice to file suit or just let it go (much easier to let it go.)
There's the off-chance they'll credit you but I would be really surprised.
If you do choose to file suit, sending an intent to sue letter with the same proof you provided in the first letter might get results. Don't send an intent to sue if you aren't actually going to, though.