You don't mention whether you're working with the listing agent directly, or with another agent, but, certainly, you have every right to expect a response from the listing side.
The agent may be having difficulty reaching the Seller, but still, you should be told this. Even if the Seller has no interest in your offer, you need to know what's going on.
Occasionally, I have encountered the situation where a listing broker who runs a one-agent office goes on vacation and doesn't leave anyone to cover his/her business. Unless your agent IS that agent, your agent should be keeping you up-to-date. What does your agent say?
If you write another offer (or present the same one again), have your agent ask to be there when the offer is presented. Good luck.
Maggie Hawk, REALTOR
Watson Realty Corp.