Iminent health Assessment Without ESA50

I filled out and sent an ESA50 in May of last year using the valuable information given on this site. I have today received a letter from the Health Assessment Advisory Service saying I must attend an assessment. The date is 3 weeks time.

This is the first correspondence I have recieved from the assessment centre since being sent the ESA50 last year. . I had a meeting with my advisor at the Jobcentre shortly after and she said she had no idea why I have heard nothing. She said she didn't even know what an ESA50 was, which I find hard to believe. I was expecting to be given a date for an assessment shortly after I returned the form.

I am confused. Is it usual to request my attendance at an assessment without a recent ESA50? Are they going to say that the last ESA50 is now irrelevant? The letter I have recieved today makes no mention of any forms whatsoever.

This may or may not be important, but I remember that my ESA50 was one day late because I was going to deliver by hand to the Assessment centre but realised it needed to be returned to another address - a PO box in Wolverhampton. I apologised on the form itself. No one has informed me that they have not accepted the ESA50 or there was any problem with it.

Any thoughts and help welcome and appreciated.