+1 @chenry is correct... 
You will need to show the item you sent and that was returned was not a purchase but was an item sent and returned for manufacturer's service. Grimm should have an invoice pro forma you can use. If you have your original purchase receipt showing the article with its purchase in state and the invoice, that should suffice.
International returned goods not NOT pay import taxes twice. Be careful to document that the item that you imported was REPAIRED and was NOT a new-stock item! Custom's agents are not service techs. New and used box/item often look the same...
If you get really stuck, and it is worth the time, you can visit your local Customs Office (get one with a service window) and request to speak with a Supervisor. (Hint - Supervisors often provide better service than the inspection officers - they deal with these issues more often.) Take your documentation, photographs, gear, etc. Be clear and simply state you are NOT an Importer, you are customer/end-user and that you sipped the item back for repair, and that CA has made a mistake - so you need this issue resolved so you can contact CA. You may get passed around a bit due to everyone's duty-schedules, so take a book to read...
Once the returned-goods importation status is clarified - if CA does not quickly correct the error, you can call the constituent services office for your US Congress person - yes, they really do help... They are on your side and will give you additional instruction...
It is easier than it may seem and should be very empowering. You may need this knowledge again...
-1 @audioman58 
"Ca is the highest taxed state in the country..." This is a merchandise issue. You rhetoric is NOT true, but typical hyper-political misinformation/disinformation - and you know it!
The facts...
Overall, in 2025 CA has the 5th highest Income Tax rate (13.5%)" <Highest Taxed States 2025>.
Interestingly, Sales Tax is highest in the South - where I live.
"The five states with the highest average combined state and local sales tax rates are Louisiana (10.12 percent), Tennessee (9.56 percent), Arkansas (9.46 percent), Washington (9.43 percent), and Alabama (9.43 percent). <2025 Sales Tax Rates by State | 2025 State and Local Sales Taxes>
Real Estate Tax: The states with the lowest property taxes are:
1. Hawaii -Average Effective Property Tax Rate: 0.29%
2. Alabama -Average Effective Property Tax Rate: 0.43%
3. Colorado - Average Effective Property Tax Rate: 0.52%
4. Nevada -Average Effective Property Tax Rate: 0.55%
5. Utah - Average Effective Property Tax Rate: 0.57%
<Property Taxes By State 2024: Ranked Lowest to Highest>
Tax are a bit of shell-game (including sales, income, and real estate taxes).
Pick you taxes, residents end-up spending about the same in most states. Stop with the politically motivated mud-slinging. Facts matter, BS doesn't...