The short answer is "Yes". Depending on the contract which is the basis of the debt, and the laws in your state, creditors and/or debt collectors may legally add on interest, penalties and attorney fees and court costs. However, you should review this matter with an experienced consumer protection attorney to determine if these fees are legit. I often find fraudulent fees added on by debt collectors and this fact may be used to either negotiate the account, or file a separate action under the Fair Debt Collection Practices Act.
Depending upon the contract for the original debt. More often then not debt collectors add what they believe to be recoverable. It may be that the additional amounts they did add are not allowable and you may have a cause of action against them for adding amounts they can not legally recover. In addition the manner in which the debt collector has gone about collecting the amount whether legally recoverable or not could have violated the law. You should seek out a consumer protection attorney and ask for a review of the additional amounts added to your original debt as well as a review of any letters and/or telephone calls you have received.