I need assistance with responding to a collection letter

I have a letter of collections from Alliance Asset Management who is representing Cash Direct Express (aka GECC). They claim I owe $778. It was for a $400 loan which I have already paid back $530. They are NOT licensed in the State of Texas.

Anyway, I never contacted them, and I received this letter:
This is an important notice. Your delinquent account has been placed with Alliance Asset Management, Inc. for collections. Per the terms of your agreement with our client the balance in full is due. If you would like to resolve this matter, as your original agreement calls for, you must remit the balance in full. This communication is from a debt collector.

Unless you notify this office within 30 days after receiving this notice that you dispute the validity of this debt, or any portion thereof, this office will assume the debt is valid. If you notify this office in writing within 30 days after receiving this notice that you dispute the validity of this debt, or any portion of it, this office will obtain verification of the debt or obtain a copy of the judgement and mail you a copy of such judgement or verification. If you request, in writing, within 30 days after receiving this notice, this office will provide you with name and address of the original creditor if different from the current creditor.

Mr. Dwyer

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So, what do I reply with? All I have so far is:

Mr. Dwyer,

I received your letter of collection dated April 7, 2011 on April 12, 2011. Pursuant to the Fair Debt Collection Practices Act, 15 USC 1692g, I hereby inform you that I dispute the alleged debt associated with account # ********, with Cash Direct Express (aka GECC) being the original holder of this debt.

Attached is a letter to cease and desist all ACH transactions...you will find the reasons why such request was delivered to your client. They are operating illegally without a license, and as such, I have paid your client in FULL. Furthermore, your client OWES me a refund in the amount of $160. I have already reported your client to the BBB, FTC & the Texas Attorney General's office.

I request that you take the following actions:
Please contact any credit agencies to whom you have reported this alleged debt, and inform them that I am disputing the debt.
Under the FDCPA laws, you are required to cease ALL collection efforts with me until this debt is properly validated, if you fail to follow the law, non-compliance of my requests could result in serious legal suits and hefty fines. I WILL file complaints with the following organizations; Federal Trade Commission, the my State Attorney General, Better Business Bureau, and the Office of the Consumer Credit Commissioner, I will be keeping a written record of all communication attempts made by your company and report it promptly if you do not adhere to the law.
Except as specifically outlined herein, I am requesting that you cease all contact with me about the alleged debt. Any further contact should be strictly in conformity with the FDCPA: It should be limited to providing me with the documentation requested in this letter, informing me that you have ceased collection efforts on the alleged debt, or stating that you are taking a specific action in relation to the debt such as commencing a collection lawsuit. Any further contact should be made in writing, and should be submitted to my home address by mail.


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What else do I say? I feel like I am missing something like asking for further proof that their client's claim is legitimate according to the laws of Texas? Please help...I need to mail this ASAP.
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Thank you!! :)