Sick note for ESA Confusion. Please help

I recently came out of work after many years. I am under the care of a mental health team and my doctor. I am 65. I put a claim in for new style ESA and a included a sick note for 6 months till next February from my Doctor. Today after three months on assessment rate I received a letter from DWP asking for another sick note to be in by yesterday. I contacted my Dr and asked for an additional certificate or my claim will be stopped or suspended. I was told that the six month certificate is valid till next year so he wont be suplying another one. I dont know what to do. My only income of £92 will stop and there doesnt seem to be anything I can do about it. Any advice will be greatly appreciated. Thanks