Yes novalis is completely correct. So long as they are paying for more than the first two places then your place bet has been halved incorrectly.
Their helpdesk is making a big play about half your stake being lost. But that refers to the win part of your bet, not the place part. There is, of course, no dispute that your 2 x £2.50 win bets are lost.
Just another minor point from their "help":
Andrae: it means as you bet £2.50, we would only take £1.75 as your stake
Andrae: the other £1.75 we take as a loosing bet
Andrae: therefore we use £1.75 as your stake
When I was at school half of £2.50 (well, it was £2-10 shillings then!) was £1.25, not £1.75.
You need to get hold of somebody at Corals who knows what they are talking about. If you deal with their helpdesk again it may help if you point at that both second and third qualify as a "place" and there is no justification to halve place bets on two competitors who tied for second place with nobody else involved. Simple way to explain this is to imagine, instead of tying, they finished second and third outright. You would then be entitled (as you are now) to the full stake and odds for each place.