NCO-MEDCLR charged twice! PHILADELPHIA, Pennsylvania

I was 22 (just came to USA) when I was hospitalized, didn't pay, two years later I receive a call from collection agency, I did forget about my dept, besides I moved, so I couldn't receive bills, any way, I paid same day after collection agency gave me a call. They never reported...my credit was clear, I was happy.

 4 years later I receive a one more call, this time it was NCO-MEDCLR collection agency, they told me I owe money for the hospital I was in 7 YEARS AGO!!! I was going crazy! How come? I did payed already 4 years ago!!! why? again??? My fault, I was shaking to much for my credit, and I couldn't prove my payment because it was to long ago, I had no record left, It wasn't fair, they said if I am not going to pay, I will have record on my credit. I payed AGAIN!!! They said they will not send a record... This time I saved every single paper in order to have prove. 8 months later they send record on my credit... and ruined it! So what I am having? I went to hospital about 8 years ago!!! Payed for this visit 2 times to Collection
agency, and end up with the ruined credit!!! My fault I was naive! Should have ask for the dept prove! Now I am older and know better how the system works, feel my self ripped off.