ESA Delay with Assessment

Hello All,

My apologies if this has been covered before, I really need some advice with this.

I applied for ESA in October 2014 and started receiving the lower amount of £72.40 per week. I was told there was a delay in getting a date for an assessment with this and my application for PIP however I have had my assessment for PIP and have my award now but still no joy with ESA.
I attended a back to work meeting at the Job Centre recently and they were surprised that I am still waiting but couldn't offer any help.
I have recently been offered a part time job of 20 hours per week and am keen to accept this but I have been told by accepting this I will have to sign off from ESA which I am willing to do however it will mean without having my assessment I won't be placed into a group and receive the difference I am owed after I passed the 13 week marker. I contacted ATOS who are still dealing with the assessment but they offered no help saying that there is no sign of a date yet and the only way it can be changed is by ESA changing my claim to urgent and fast tracking me, needless to say ESA are unwilling to do this as they are keen for me to come off the benefit and save themselves a few hundred pounds!
If I take the job I lose around £300 which I am genuinly entitled too and after not working following a serious operation I really need, if I wait for an assessment which could be weeks if not months away then I lose the job offer, seeing as the government are keen to get people off of benefits and back to work surely there's something that can be done?
I'd be grateful for any advice please? Thanks.

I thought as much, thanks for the reply. I did think about asking for less hours but unfortunately the training involved for the position is 6 weeks long and is strictly 20 hours per week.