I received a Memorandum of costs after judgment, acknowledgement of credit, and declaration of accrued interest from a Lawyer.

These things do have a tendency to grow and fester, and I suspect your not having had a lawyer to represent you has contributed to this growing problem. Trying to deal with it by yourself is likely to lead to more of the same. It is often false economy to try and avoid legal fees where good legal advice could possibly have helped prevent the problem.
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Disclaimer: California attorney Robert Miller has practiced for over 45 years and restricts his practice to real estate and probate matters in the Central District of Los Angeles. Any opinion expressed is for general informational purposes only, no attorney-client relationship is intended or created by this answer, and no action or inaction should be contemplated without first employing and consulting with a competent attorney convenient to the questioner.

A memorandum of costs after judgment means that the plaintiff has a judgment against you, because a response was not filed by you or your lawyer, to protect against that occurrence. You should consult immediately with a debt collection DEFENSE lawyer and review my blog posting that explains the options when a default judgment is obtained by the plaintiff in a debt collection lawsuit. My blog is linked, below. In particular, your next move will need to be setting aside this default judgment promptly, either because you were not properly served with the lawsuit, because you had an understanding with the plaintiff's counsel that they would not seek a default judgment while you made the payments, or because you made a mistaken understanding that the payments meant that they would not seek a default judgment. Being prompt is the key, I doubt a phone call will be any use and often the phone calls are twisted around to make it appear that you agreed to whatever they want, so they can tell the judge what they claim you said.
Robert Stempler (please see DISCLAIMER below)
www.StopCollectionLawsuits.com
www.facebook.com/SoCalConsumerLawyer
Twitter: @RStempler

Call first to see if they will deal, if not then lawyer up.

Did you know that someone has a civil money judgment against you? I suggest you look up the case on the court's website; input the case number (from the Memo of Costs) into the Civil Case Summary webpage.
If you've defaulted on your payment plan, the plaintiff probably filed the Memo of Costs because he/she/it is requesting that the court clerk issue a writ of execution. And the purpose for the WOE is to levy your income and assets. In other words, the plaintiff is probably preparing to levy (take) the money from your bank account (if you paid by check, plaintiff knows your banking info) and/or to garnish your wages (if plaintiff knows your employer).
You can call plaintiff's attorney to try to negotiate a new payment plan. Make sure the plan is in writing AND includes a statement that "Plaintiff agrees to stay execution of the judgment for so long as Defendant complies with the terms of the payment plan." "Stay of execution" means plaintiff will not try to enforce/collect the judgment.
I do recommend you consult with a debt collections defense attorney. His/her advice may be well worth the consultation fee!