Working tax and ssp

i have long term depress and have fibromyalgia also narrowing of the spine that I may need to have an opp I have been off work since 12 dec and don’t expect to return for a while I have the higher rate of pip both elements and working tax and worked 18 hours per week after having to reduce my hours cause of ill health my work pay sick pay for 5 months and then the 6 month half pay they told me yesterday that my wage is going to drop to half end of this month and then have to claim esa which I have never done before I could not understand why my sick pay was reduced so quick they told me that since 2016 I have will have been off 28 weeks in total I thought it was meant to be 28 weeks straight but I thought ok what about my working tax credits is that now going to have to stop or not cause it states on there web site you can claim for the first 28 weeks of sickness so I would take this to mean that I should be ok till June can anyone advise pls