First, as an SFR (short sale and foreclosure certified agent), I CERTAINLY hope you are doing this using a Realtor and that the seller of the house is also using one. WAAAY too much paperwork, and follow up is necessary to make a short sale get to a closing if no one knows what they are doing. Are you and the sellers using an attorney? Perhaps he/she can get some information for you from the sellers attorney or their agent.
Second, what do you mean by the "seller won't respond?" . Have they not entertained your offer at all? They don't really have to answer you at all, though common courtesy says they should let you know if the offer is not accepted.
Have they signed the contract and it's at the bank, but no one's told you if the BANK accepted the offer, which is why you want to contact the bank? (which BTW you cannot. Only authorized people representing the seller, like their agent or attorney, can contact the bank).
Third, I have done numerous short sales, and the banks are not as lenient in the amount they are willing to "lose" but it depends on a few things . Most of the banks I have dealt with will only approve the sale if the house is selling close to, if not AT, current fair market value. They do a market analysis AND an appraisal, so your offer may be too low. What makes you think your offer is a "great offer" when it's not at asking? Maybe the sellers know what the house is worth at fair market and priced it accordingly.
If the sellers already signed the contract, it can take more than a month for the bank to reply one way or the other. It's about the communication between seller and buyer (or their attorney/agents) for updates, even if that update is "it's still with the loss mitigation people".
This really all goes back to both buyer and seller using or not using a Realtor.
Since you should have no access to the sellers personal financial information, you will never know if there is more than one lien (which makes the short sale even harder), and you really don't know how much the bank is going to "lose".