NHS Invoice

[sarwarge]

Dear Members,

I am seeking urgent advice regarding a complex issue I am facing. Here is the background:

I came to the UK on a Sole Representative visa, but unfortunately, my extension was refused. I subsequently went for an Administrative Review.
During this process, my daughter, who was a dependent on my visa, turned 18. She received an NHS invoice of approximately £2,400 for treatment of anemia. The invoice states that she came to the UK on a visitor visa and therefore must pay for the treatment.
I informed the NHS that she is my dependent, I had paid the IHS fee, and we were on C2 leave at the time. They responded that they would contact the Home Office for clarification.
Unfortunately, my Administrative Review was refused in November. I have since applied for a Skilled Worker visa, which is currently under consideration for myself and all dependents.
Today, my daughter received an email from the NHS Finance Department stating:
The Home Office confirmed that the invoice is chargeable.
The application refusal was upheld, so the invoice stands.
I am extremely concerned about this situation. I have a few questions:

Is there any possibility to challenge this invoice, especially since we were under C2 leave, had paid the IHS fee, and my daughter was my dependent at the time of treatment?
What steps can I take to resolve this without paying such a significant amount, especially as I am awaiting a decision on my Skilled Worker visa?
Has anyone dealt with a similar issue or has insights on how to approach this?
I would be very grateful for any advice or guidance you can provide.

Thank you in advance for your help!

Best regards,