Tesco conversion always states please allow 28 days for miles to credit. Admittedly this usually happens sooner but does not mean it always will. And Tesco is one of the most reliable partners I have used for mileage conversion so it is a safe bet they will show up (here's looking at you Shell, e-store, Avis etc.)

Did you get your Tesco vouchers early Kirky and your 28 days has elapsed?
If not then please dont throw your toys out of the pram and make such statements without any facts to back them up.