Collections companies buy debt for a fraction of the face value of the debt (as little as 5-7 cents on the dollar), and you can often settle debt for a fraction of the face amount (perhaps 10-25 cents on the dollar).
But there are several considerations. Do you owe the debt (is it a legitimate debt), can you afford to pay the debt, what is the age of the debt (remember, there is a statute of limitations on debt, varies by state), and what are the consequences of non-payment or settlement of the debt.
Rather than confirm that you owe the debt, tell the debt collector that you need proof that the debt is yours (you should do this by certified letter). Be careful not to confirm the debt, or agree to pay it, or make any payments (yet).
You said that your doctor ordered the product for you.
You said the company sent you a product (you have the product).
Once you have confirmed that the debt is yours, you should determine the age of the debt (when was the last time you paid on the debt). Each state has statute of limitations on debt, depending upon the age of the debt (this is why it is important not to send the collector money until you have verified the debt).
You did not state when the debt was incurred (assume under SoL).
Ask yourself whether you can afford to pay the debt. The amount of the debt, and your ability to pay, and whether you want to avoid the time and expense of dealing with the collector (they are trained to be annoying) are all factors to consider. You should also consider the negative consequences (credit score effects), and whether the cost of a derogatory entry is worth fighting the debt.
You did not explain your financial situation; paying the $55 may be trivial, or it may be a hardship.
Before you settle any debt, you should send a letter (keep a copy and proof you sent it, certified), and demand that the debt collector provide proof that you owe the debt. Often this proof does not exist, or is insufficient to gain a judgement (you would need legal help here). And should a debt collector agree to settle the debt for a lower amount, you need to get that agreement in writing. Be aware that when you settle a debt, the collector can (and will) send you a 1099 for the portion of the debt which has been forgiven, and can report to the credit bureaus that you settled a debt for less than the full amount (negative mark against credit). Derogatory credit items will haunt you for years.
Decide whether saving $20, $30 or even $55 is worth the trouble. Probably not.
Learn from this.
When a company sends you something you did not order, contact them, and send it back or demand they pay shipping, and send them a letter demanding $5/day storage and $20 handling fee to ship it back to them.
Disclaimer: Heed the insane ravings of a deranged heretic at your peril... hire a lawyer.