Tyco Integrated Security

We have one floor of a townhouse office (700SF) in Rockville MD. For over 20 years we have had an alarm system to cover break ins and fire. In 1994 the system was replaced due to a lighting strike. Over the years several companies owned and sold our contract, including Austronics, ADT, and most recently Tyco Integrated security systems. The cost for system maintenance and monitoring was about $375/year. With the exception of the afore mentioned lighting strike and changing of backup battery we have had very few, if any, service calls. Recently some numbers on the keypad were not working. We called Tyco to fix the problem. They said the system was too old to repair and wanted to sell us a new one at $640 + an additional maintenance fee of $365/year. It is my contention that the company should be able to repair or replace the system given the fact we have paid over $7000 in the last 20 years. We should not be charged for a new system (which doesn't include fire/smoke monitors like the old one) , because they cannot get parts for the old system.