When transferring a subscription from one car park to another, the first subscription remains active until the end of the 2-days free trial of the second parking ends. This gives you access to the two car parks during the period.
An automatic reimbursement will be credited to you for the unused days in the first car park as soon as the subscription for the second parking starts. (i.e. at the end of the trial period of the new car park).
At the end of the 48-hour trial period, you will be charged for the new car park, but also reimbursed for the unused days in your first car park (pro-rata reimbursement). A refund takes an average of 5 working days to appear on a bank statement.