Paying for a service that is not being provided

The tracking device has not been working since January. I informed Altech Netstar and nothing was done. After their accounts dept made a mess of my banking details, debit orders became a problem and I received mails threatening legal action. The amounts were all paid in full as the fees were not the problem on my side. I responded to the last mail I got about this saying that I would not pay until the device had been fixed. I was contacted and told that an attempt would be made to refund me for the 6 months I had paid for a faulty device and that the tracker would be fixed. Nothing happened and a few days later, I woke up to an SMS from my bank telling me the outstanding money had been deducted by Altech Netstar?! So, they can threaten legal action & do nothing about customer dissatisfaction but can miraculously correct banking details (after more than 6 months) to TAKE money I said I would not pay. When I mailed the rep back to say that I considered this an act of theft, I got no response but had an influx of calls from customer reps to make arrangements for the device to be fixed. It is now fixed, but I would like to know how I will be compensated for all I have had to deal with.