The firm says the decision was taken to close the platform from Friday to today “based on the lessons learned from the first phase of migration which happened back in April.”
The firm added: “We wanted to do all we could to ensure the process was carried out as effectively as possible.
“We first communicated this with users in an email sent on 7 December and followed this up in our monthly bulletin issued on 14 December.
Ascentric publicised the closure times on the login pages of both platforms two weeks in advance and it was included in the IVR message from the start of last week.
The company says users were also sent a reminder email on Thursday.
Ascentric head of sales and marketing, Justin Blower, said: “Our intention has always been to migrate clients to the new platform efficiently and we therefore took the decision to take the platform down for two business days to allow ourselves time to do that.
“We learned valuable lessons from the first phase of migration that we carried out in April and our approach has been informed by this experience.
“We continue to be open with our users about our approach and began communicating with them about this in early December.
“The majority have been supportive of this approach.”
He added: “This will be the last big migration that we carry out and we will only have a very small number of clients yet to go through this process.”