Sodexo Childcare Vouchers - expired?

I just checked my childcare vouchers account with Sodexo and found that a few thousand pounds have disappeared from the balance!?  I collected the vouchers when I worked in an office job.  I now work from home and have not needed childcare for a few years.  Last time I checked I had around £3000 - 4000 in vouchers.  Now I have £1200.  The small print says that vouchers can expire, but when I left my employer, I remember asking this question and being told they would not expire!  I was planning to use them to pay for my daughter to attend Preschool and then in a few years After School Club.  I thought I could use them until my daughter was 15 (she's 3).  Anyone know where my vouchers could have gone and how I can get them back?  ... I'm intending to phone Sodexo on Monday, but feeling a bit sick at the moment.  Thanks!