Welcome to the community @MissMuffitt,
I moved your post here because it is more about Sendles processes handling your problem than them necessarily being shonky as I read their web site T&C.
Could you be more specific on what you mean? Did you make a claim that has been ignored?
I presume you made the claim via their dashboard? Their requirements for the photo are a bit strict, and I can imagine difficult to achieve in some circumstances.
How long have they gone missing since you lodged your claim? The show a service level of 7 days response.
Note that although they
Step 5 on their claim system includes (my bolding) ‘you’ll need to include relevant info about the parcel’s contents and proof of its value (like a receipt, invoice or a statutory declaration)’
Have they rejected a stat dec? Considering the age, item dependent it could be very valuable, or not valuable at all excepting for sentimental value that is rarely compensated for. You could augment your claim by googling for values of your item, or a similar item and may get lucky to find something easily.
If they have rejected a stat dec I suggest you copy their instructions and their T&C in case they modify them, and read about your sights under the Australian Consumer Law for services and proceed to follow the process to send them a formal letter of complaint.
This Choice report is a good place to begin.
Anything done by email, voice, etc, needs to be kept as evidence should you go to the ACCC/Fair Trading, and note that anything excepting a formal letter of complaint is nothing but what I call ‘idle chit chat’ as regards to your claims. If one goes to the ACCC/Fair Trading prior to sending a formal letter of complaint, they usually advise you to do that and come back if still not resolved, so a letter is advised up front.
For additional advice you can search the forum for ‘letter of complaint’ using the community search, upper right.
Posting a bit more detail about your problem might result in others providing experience or advice, and regardless, if you make progress please add that.