PIP

Hi
I had my PIP assessment via ATOS at one of their centres on 12/02/16.
On 26/02/16 I received a letter from ATOS saying I 'm being assessed in my home on 09/03/16; it read as though it was a first time assessment. I telephoned ATOS explaining I'd had an assessment etc. The man on the telephone said they must want further information/2nd assessment/there had been an IT issue! I asked him to find out please. After much persuasion on my part he went off to fine out, returning to say it was an IT issue. I asked him to expalin and he said that it must have happened when the assessor was submitting the report to the DWP. I asked him why they'd not 'saved' it and he said that if the IT issue happened in the submitting process then all data will have been lost.
Have you ever heard of this before?
Do I have to agree to a 2nd assessment as it's their 'fault'?
I found the first assessment and all the organisation that required very anxiety inducing etc, and now I have to go through it all again. He did inform me they were making it easier for me by allowing it in my home father than making me go to the assessment centre again!
Do I have a right of appeal/refusal on thhis matter, or will they then just say I refused assessment and disallow my claim? (I'm, hopfully(!) migrating from DLA to PIP).
Many thanks, and I look forward to any comments and advice

Thank you for your reply.
Should I reply with a complaint ASAP and use that as a basis of trying to get them to assess me via paper only in order that I don't have to endure another face to face assessment? Or do I just complain about their inability to send a report to the DWP and 'lose' it in the process (although I still don't understand how they don't have a 'saved' copy of what they were in the process of sending to the DWP and then just resend it!) but perhaps I'm being thick there as it doesn't work like that!? Or am I better waiting until after?
The entire process has been dogged by issues with them ringing me the day before my first one and asking me to attend two hours earlier as a member of staff had called in sick!
I'm not sure what to do at all here really, push for a paper only assessment or go through the assessment again. When would you advise I make a complaint about my entire experience at the hands of ATOS?
Many thanks; any adive greatfully received

Hello again
I've contacted ATOS again today to clarify how my data had got lost and they now say the reason they want to do a second assessment is because they want ot do a 'fair assessment' and to check 'everything has been done correctly/make sure evrything is correct'. Have you heard of this before? It appears to get more bizarre by the minute, with a different reason both times I contacted them! I thought you had an assessment and then they made a decision, but obviously not in my case.
Many thanks for any advice/comments.