Exempt but now being threatened!

I bought my apartment in January 2013. When I found out that the legislation was written in such a way as to leave me exempt until 2017. I wrote to LPT and made a case. In January I received a letter informing me that I am exempt. Now I have received a letter informing me that I haven't paid and they are contacting my employer so as to make deductions. Hope disorganised are these people? Surely this is a breach of the Data Protection Act?

I presume the they in this case is the Revenue
The Revenue have the right to proceed as you outline.
Rather than worry about the DPA I would carefully check to see that the name, address and reference number on the letter is exactly the same on both letters and that the property at issue is the one you bought in 2013 and that the tax being sought is for the same period.

I would contact Revenue re this: you can find an email address for your tax office on Revenue.ie