Aurora,
It all depends on the provider. I have one psychiatrist who is still trying to track me down for payments 2 years later. He has not yet sent me to collections even though I haven't been able to make any payments (insurance paid 80%, but I've paid nothing). In December, I got a "Final Notice -- if account is not paid by December 31, this account will be sent to collections". Well, it has not been sent to collections yet.
On the other hand, the blood place sends you to collections if you are 2 months late, even if you made a partial payment if that partial payment was less than your payment plan.
So it really just depends.
I think you really do need to find a way to see an oncologist, though. Please do talk with your provider at your next appointment & explain what is happening. Tell your doctor that you would like to continue seeing him/her but are unable to keep to your original payment plan. Ask if s/he would be willing to accept something less than that amount. If s/he says no, they maybe you can ask for a referral to a lower-cost provider.
There are a lot of programs that offer assistance to cancer patients. Perhaps one of those programs could help you. Here's a link:
http://www.cancer.gov/cancertopics/factsheet/Support/financial-resourcesFeel better & hang in there! Everybody has bad days. Try not to let it suck you back into deep depression. I know from experience that it is not easy to not give in to the negative thoughts, but I believe in you. Things don't have to get worse, so try to believe that they will get better. I will be hoping & praying that they really do get better for you.
peace & blessings,
Frances