hi,
first of all, according to Turkish Law, lawyers can not establish firms. They must prctice individually and they are also responsible from their actions individually. There is no legal entitiy as "Law Firm" in Turkish Law. What I am trying to say that the lawyer that you have made the contract with and the one that you made the payment to (briefly the one wwhose name is written on the "power of attorney" is responsible of solving your legal problems.
Also a lawyer can not establish more than one office in Turkey. He can have just one office. What I understand from your inquiry is that you gave a power of attorney to a lawyer in a major town and your lawyer authorized another one (the local office).Your Lawyer's ceasing business with the subsidiary office does not cancel your contract with your lawyer. He is still responsible to you.
But this advice depends on assumptions. You need to give more specific details about your relation with your lawyer.( the one you gave the power of attorney , the one that sent you the notice etc.)

Then I can advice more.