Tesco partner vouchers

So we got our £25 Tesco vouchers exchanged for £75 Le Shuttle partner discount vouchers.

We booked a 5 day return and added our voucher to get the total of £207 down to £ £134, or so we thought.

Then Eurotunnel says NO you cannot spend this voucher on Special offers only on standard fares, which then worked out at a total of £184. So that's my £75 voucher reduced to.. the original £25!!

Any more takers for this?

What a c0n.