Notice of Dispute filed 3 mos ago- No response from AT&T- Sent to collections

I am a former ATT wireless customer with a family plan. After several years of nothing but problems with my service and poor customer service experiences I ended my service. I could go on and on, however it would take too long. I'm an old man and would probably be dead by the time I finished explaining. The final straw was last Dec when I called regarding setting up a new plan with data. ATT rep first wanted to update my account info and in this process we discovered I was being charged for a line that I had diconnected a year prior. I had been charged for it all along-outrageous! Rep transferred me to another dept. and I spoke to someone who I could not understand. I am 45% deaf and couldn't understand his accent. Eventually, I told him to have someone call me later- I had a prior engagement and couldn't spend any more time on the phone. No one called me back. I called a week or so later, and after explaining my issue to several different reps and getting transferred, I was finally put on hold. No one ever came back on so I finally hung up. I was mad and started looking into other cell phone providers. I never had an issue that wasn't resolved quickly with the service provider I had before ATT bought them out. With ATT I had nothing but issue after issue, with junky phones, bad reception, lacking customer service, etc.- none resolved. Long story short, I found another provider and ported the numbers I decided to keep. In March I spoke to another rep and told them I would not be requiring service after that billing cycle. Tried to talk me out of it but by then I was fed up and hung up. However, still received a bill for the next month when no service was used. After receiving this bill, I spoke to another rep (this was in May), who again, I could barely understand. I informed her I was disputing some of the charges, she told me she couldn't help- I would have to file a Notice of Dispute. My daughter helped me figure out what the heck a Notice of Dispute was, and I sent this certified mail with return receipt, along with a letter and several pages of information regarding the many issues I'd had and details of the charges I was disputing.  Told them very nicely that I wanted to pay what I owed, but was not willing to pay charges for services not received. I also requested they communicate with me in writing due to my hearing difficulties and hours of business- I run my own business early morning til night and can't spend hours on the phone during the day rehashing the same things I've already explained to 5 different people. I sent this on 6/6/14 and received the certified mail receipt signed by an ATT employee dated 6/10/14. No word from ATT since- 3months!!! No written communications, no phone calls, no emails, no response to my notice of dispute- until, I received a letter from a collection agency last week, which includes all charges for disconnected line and a month of non-service on other lines!!! I am livid. I have excellent credit, and this better not find its way onto my credit report or effect my business dealings in any way! I will dispute this with the collection agency of course. My wife also suggested filing a report with BBB, which I will likely do also. My good friend is an attorney so I will consult with him also. However, I thought I would come on here and inquire if anyone else has experienced a similar issue and how or if it was resolved without seeking legal remedy. That is a lot of hassle I'd rather not go through, but I will if I have to, not because of the money( it is a relatively small amount), but for the principle of charging customers for service they honestly were not provided and poor customer service to boot. I didn't fight in a war and become disabled for the freedom of corporate crooks to rob me. I would have remained a loyal customer to ATT, despite some issues, had customer service been better. Advice?