You can attempt to explore through discovery whether the plaintiff is in fact representing Capital One or has acquired the debt. Consistent with the discovery rules of the court in which the suit was filed, and assuming that court permits discovery, consistent with the rules you can seek a copy of the relevant documentation including any past assignments of the debt. You would likely want to raise the issue of standing as one of your affirmative defenses when you file your answer. If the case goes to trial, or if you bring a legally sufficient motion that requires them to submit evidence in support of their response, they will be required to present evidence to support their position. There's no automatic reason why a summons and complaint would include documents; for most actions that's not necessary.

