Plus the price is excessively high. That appears to be some sort of list price which it is not expected that anybody is paying.
And even if part of that price included one month of supplies, how much could the supplies cost? $150~200?
Tandem generally receives about $4000 to their bottom line per pump sold (via insurance direct or via distributor any method). Cash price for an X2 from Tandem should be right about $5000. (USA pricing. International different pricing.)
There is no possibility that Kaiser is paying Tandem $7495 for an X2 pump.
In any event - none of that should be relevant here. This is not your problem.
In my experience, providers generally have 1 year to complete billing to the insurance company. I have had a few times where the provider failed to bill the insurance company in a timely fashion (ie - over 1 year). The insurance company informed us that the contract between the insurance company and the provider accounts for this possibility and the provider is contractually prohibited from billing us for the services rendered or equipment provided due to this situation.
Which I believe is the same thing that Kaiser told you? Tandem failed to live up to the terms of the contract between Kaiser and Tandem. This is on Tandem. Very bad business practice for any company. Hopefully this is an isolated incident and they (Tandem) corrects whatever business problem they have.
Bottom line this is not your problem.