You can check your current membership and account credit status in My 48. What does it say? If you buy 2 memberships, the second one will stack up and start once the first one has expired.
If you are unable to buy your membership via the website, you can also buy membership by text, see here. Note that you need to have already enough credit on your account in order to do this.
If you still experience any issue, you can also contact the 48 agents via this link, and they can take a closer look at your account.
