The short answer is no, your employer cannot do this.
If you received a new contract was it just a letter of notification of new hours, or was it a full letter addressed to your with two copies, one of which you signed at the bottom and gave back?) then it can't be claimed it is a simple clerical mistake - especially as you have transferred on the same base salary. I believe they are therefore duty bound to honour the date-dated hours worked so far.
However your employer could ask to amend your contract, giving you notice that it wishes to do so. This should be a discussion, not a demand, and you have every right to refuse it. You might, for example, prefer to be back at the old depot if the deal is not what you were told it was. You could state that you prefer this to happen, and see what they do next.