Terrible service

My daughter had blood tests done, account was submitted to medical aid, who declined payment. I had to call and email Lancet numerous times before I actually received the account to make payment. When I received account, I asked Lancet if they would give discount for Cash payment customer ( which I received with other labs) they then increased the invoice amount. I have emailed on numerous occasions asking that they revert invoice amount to original invoice, which they were originally going to accept, I feel it is heartless and ********* to increase an invoiced amount when somebody is asking for assistance and a reduction. Instead of replying to me they sent my account ( for the difference - I paid original invoice amount - which by the way, was the amount they charged when I utilised their link to payment.) to their debt collected. Only now responding to my email again advising they cannot amend invoice, strange how they were able to amend it before, but now they can't. How can they be so heartless when somebody is asking for assistance not being able to afford the original amount and now wanting more.