The 150% charge does sharpen the mind a little.
In this circumstance, you probably need to work out what is going to cost you least and follow that course of action quickly.
So far having not lived there for 12 months you have incurred a year's worth of extra mortgage payments, what is the value / opportunity cost of not getting a quick sale?
As has been said before every house will sell at the right price and sadly the right / market price doesn't always line up with the vendors view on things.
If I were in your shoes, I would be looking to get shot of the house asap or to get it rented asap. Council tax is expensive as it is and at 150%, it is really bloody expensive.
If you were to rent it out, you might be able to go down that route without too much expense. Get some cheap and bland paint and paint the walls of the house and see where you can go from there. You need to have a gas safety certificate (if it has gas) and there will be agents fees, but if should end up costing you less than it does now.
As it stands you are paying 100% of mortgage and 150% of council tax. Even if you rented it out for less than the mortgage cost you, you wouldn't be paying the council tax and you wouldn't be bearing the full cost of mortgage.
Out of interest, have you got / been able to switch over to an interest only mortgage for this property, as this may ease the mortgage burdon each month.
Hope you get it sorted soon.