I've just been served by a debt collector what can I do from here

Assuming you mean that you have been served with a lawsuit, you are generally going to have 30 days from the date of service to file a response. Depending on the size of the debt, you pay want to retain an attorney to defend you. Even if you do owe the debt, often times an agreement can be reached to settle for a reduced amount and/or to agree on a payment schedule that makes the payments manageable.   Thanks,Jon