Unhappy Customer

I received my sim card on the 23rd of April. I put the sim in my phone to run a speed test and it registered at less than 0.5 Mbps Download and 0.0 Mbps Upload. I waited a day and did the test again. Still no Joy with the speed test. The most I got on Upload speed was 0.1 Mbps. Furthermore, I cannot change the payment details to a different bank card as I cannot leave it to take from the Credit Card. I am trying to change it to my Debit Card and it just refuses to accept the details of my card.