Don't think I can be much help but unless something has changed in the past few years, I don't believe it's because of you applying too quickly. I applied for the Reserve within 2 months of getting the Charge and was approved at the time.I'm unsure. Before I applied for it this month, I called through to complaints asking them to help. They spoke to new accounts, and new accounts said there is no reason on their end as to why if I apply this time, it would be declined. And yet here I am...
Can't remember but was it advertised in the welcome material for the Charge that the Reserve is complimentary? I remember seeing it in materials they sent out about the changes to the Charge after the fee increase. Might be pushing it but perhaps you can point out that the materials say the Reserve comes with the Charge, albeit a separate application, which was part of the reason you applied so they should manually approve you (don't even know if that's possible though)?