As treatment was likely under £500, your visa won't be refused. But processing may take much longer while they wait for your records to see what treatment you received and what the cost would be to ensure it's under £500.
Where were you treated? Maybe we can help you get a hold of the proper trust to get the paperwork to help things along.
When I first moved here I didn't realise I could use the NHS under my Tier 2 visa and an urgent care centre had no problem charging me and this was in 2010.
You are my absolute champion and I am your biggest fan.
So I was treated at Finchley's Walk In Centre
I will retrace my steps since then so you don't do the same thing I did:
-I physically returned and spoke to the desk where I was initially processed and they referred me to the following number:
Information Governance 0208 102 5005
-They referred me to their email CLCHIG@nhs.net
-They responded having me contact the NHS Business Service Authority (their website was useless, so I called them) 0191 232 5371
-They Referred me to the Overseas Health Department 0191 218 1999 (who said they only dealt with UK citizens in other parts of Europe needing help)
-They sent me over to some Financial department which sent me to NHS England at 0300 311 2233
-They sent me to another Overseas department which I didn't write down their exact name, but they are different at 020 7210 4850
This gentleman (named Ian, I believe) referred me to the government website where I quoted from previously. He said that if I get denied, refer them to that part of the document (It's page 12 or 13, and I can link to it if necessary)