USELESS APP & NO CUSTOMER SERVICE!

Ever since they decided to tinker with their App,it has been a TOTAL PAIN IN THE @$$!!! They sent out an SMS saying that no Cash Back Rewards will be available from the 23rd - 30th June,but that all Cash Back Rewards would be re-issued after that. More than a week later,& The App doesn't work at all. I call them,& am told that someone from I.T. will contact me A.S.A.P. It's now 3 weeks later,& a whole month since their new bigger & better System was supposed to be "Up & Running",& the damn App is ABSOLUTELY USELESS!!! IT DOESN'T WORK AT ALL!!!!! I have un-installed & re-installed it several times,with no results. I can't even check my Credit Card Statements. Worst of all: - I HAD 2,IF NOT 3,CASH BACK VOUCHERS,WHICH HAVE ALL VANISHED INTO THIN AIR!!! THIS IS UNACCEPTABLE!!!!! FIX THE DAMN THING NOW,& GIMME BACK MY CASH BACK VOUCHERS!!! How can you justify these issues after a whole month past your deadline??? (I don't why I'm even bothering to write this,as they are not replying to any of the complaints).