I am not sure that a list agreement without an end date is valid. I would call this agent directly and inquire. Sometimes things such as this were due to misunderstandings, and if this is the case, your agent may work to fix this. If you do not get a satisfactory answer, I would call his/her broker.
It sounds like you are not satisfied with your listing agent and are looking for a way out of the listing agreement. I would recommend just telling your agent or your agent's broker that you are not happy, list the reasons why, and then ask to be released from the agreement. I can call the TAR legal hotline and ask if the fact that the agent did not put a start or end date on the signed agreement makes the agreement void and null. Has the agent produced a full-priced offer? That would make terminating the agreement more difficult. Best wishes that you resolve this and sell your home as quickly and as painlessly as possible. ~The Hill Team