Mayo Clinic Sending a bill to a collection agency when they've been receiving regular payments Rochester Minnesota

I was diagnosed almost 3 years ago with terminal cancer.  I had gone to the Mayo Clinic in Rochester, MN to see if there were any treatments or clinicals that could help me.  There were not.

Then came the bill which was for several thousand dollars.  I am not a weathy person so I could not pay the full amount at once.  I began making payments and never missed a month.

I began receiving notices from the Mayo Clinic that my bill had not been paid in full yet.  I continued to make the monthly payments and did not miss a month.  Today I received a notice that my bill had been sent to a collection agency.

I had whittled a bill of several thousand down to $1,025 and that still was not fast enough for them