You shouldn't need a lawyer to address this. The County expected a change of address for your business license and your business taxes, and may not accept the fact that your business ceased operating in the County several years ago.
You should try sending them your corporate dissolution documents, as well as proof of your new address as of 2008-2009.
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I am going to make some assumptions because you don't provide a lot of information. I'm going to assume that your small business was not incorporated, that it was you operating under an assumed name (a dba). I'm going to assume that the kind of taxes you are talking about are "business personal property taxes". I'm also going to assume that the summons you refer to is not a summons but is a lawsuit for unpaid taxes. I feel good about that assumption being correct. First, you MUST ANSWER THIS LAWSUIT IN WRITING BEFORE THE DEADLINE. If you don't they will get a judgment against you by default and the game is over. DO NOT MISS THAT DEADLINE. If you do you will become liable for taxes that you do not owe. So, take it to a lawyer NOW. If, you cannot get a lawyer immediately then you can file the answer yourself just to avoid a default. It will need to be re-done later by a lawyer but file a written statement with the court (the instructions are on the lawsuit) that says "I deny everything. I was not in business on these dates." The deadline is determined this way. Take the date you were served, start counting on the next day and count 20 days (not just business days, but 20 calendar days). Then go to the next Monday after that 20th day. That is your "Answer Day". It is the date by which your written answer must be filed with the court. After you have done all that, then you can start talking to the lawyer representing the county about how you were not in business in those years. It won't be easy. They don't just take your word for it. The problem is that you probably failed to "render" your business personal property for the year in which you ceased business. So, as far as the Appraisal District knows you still are in business and you still have all the assets you had previously. You really would benefit from hiring a lawyer.
DISCLAIMER: This is not specific legal advice and does not establish an attorney/client relationship.
Orsen provided a great answer and made some valid assumptions based upon the short statement of issues above. If the amount in controversy is anything more than a nuisance value to you, and it likely is, you would greatly benefit from taking all relevant documents and laying out all supporting facts to an attorney in an initial consultation. This is not the kind of thing you want to handle yourself especially with an amount in controversy that gets your attention.