I am not sure what state you live in, but in california the fee to sue them is around $16 for small claims court. What i would do, is to write the collection agency a letter disputing the claim and ask them to provide you with proof of the bill within 15 days. I would also call the doctors office and dispute the claim with them. forget the collections agency and go for the doctor. as we all know that doctors time is very expensive, let the doctors office know that you will file a claim in small claims court against the doctor himself in the amount of $5,000 dollars (in california) in or about 15 days from now. with the doctor himself named as defendant. if no response.... go ahead and file... it is actually too easy to do, and under the part where you state your claim write something to the effect "I will dismiss this claim if the billing is corrected and removed from collection agency and all negative items removed from my credit reprts in regards to this matter". this will get you immediate action from the doctor...... as he is not going to show up for court for $45, and if he doesnt show..... you win $5,000. so when they call you to let you know they have taken care of everything and you can now dismiss your claim....PLEASE!!! let them know you expect the $16 for the filing cost. you will be amazed of how well and how fast that works!