Lol @ writing a book.
The first offer is always a little less than what they are prepared to part with. However, are you sure you have got the correct and current value of your vehicle correct? Depreciation doesn't differ from each insurer so you would probably receive a similar amount regardless of the insurer. The settlement of a claim, or series of concurrent claims (such as the stereo) should be done promptly. This aspect of insurance is what, ultimately, insurers are judged upon by joe public. Unfortunately people are too quick to accept a quote on the basis of price and when it comes to making a claim they are let down. This is due to ill-researched profiling and recommendations. How often do you hear "Oh I'm with 'X', they're really cheap! Give them a try!"? They're ridiculously cheap for a reason and if the person recommending you had to make a claim, the other side of the coin would be revealed - ie. "I was with 'X', don't go near them. They're cheap but hard to deal with!". And so the story unfolds...!
Although the quality of staff (by knowledge) at Hastings is not very desirable, there are a lot worse companies out there in terms of initial price:claims handling ratio. Sometimes things slip through the net and in any business there will be disgruntled customers. It would appear you are one of the unlucky ones.
Finally, I'd just like to add that a stolen car used in a ram raid, which is subsequently written off, is far from a 'very open and shut case'. In fact it's at the other end of the spectrum!
Good luck, and let us know how you get on!