Medical Assessment Cancelled - Advice Needed

I was due to have my assessment tomorrow morning but today I received a phone call saying that it had to be cancelled as the Dr is not available. He said they would just put it down as a cancellation and I would receive another appointment in due course?. My worry now is I am in the 12th week of the assessment phase and would hate to think that by them noting it down as a cancellation, that it is not my doing i.e not turning up etc. How will this now affect my ESA and should I do anything? Has this happened to anyone else and if so what is your experience of what happens next or where you suddenly liable etc. It's a bit frustrating as have waited so long and then the last minute cancelled!

Thanks Gordon for the advice.

I rang the centre this morning and they said it is not in their remit to send out cancellation letters although did advise me that it is logged on the system as their doing. I also was handed to the person that actually called me yesterday, he gave his name and fully explained that they didn't have a Dr available for today so had to cancel 5 appointments. I re-confirmed my worry that I don't want it ending up being my fault for not attending and also recorded the call in case of any comebacks. He did say I should receive another appointment within 2 weeks. Fingers crossed I do.