I have been sent the UC50 & ESA50 forms

Hi I applied for ESA and UC for the housing benefit early September and was sent the UC50 Capability for Work form at the end of September. I started filling it out and became ill again in October so I called the UC and told them, the guy I was talking with said he would make a note on my account that I would be sending the form back two weeks late.
Then today in the post I received another Capability for Work form but at the bottom the only difference is the code which is ESA50. I need to know i I need to complete both forms? I called UC/ESA today the man I spoke to said he had never been asked this question, he spoke to his colleagues and they didn't know either. So I really don't know what to do for the best! The guy said to maybe just send in the first one as I would still be applying for the benefit but I don't know if to complete he other form too in case they sent me the first one by mistake? Any ideas please? thanks