Why are courts allowing Capital One to file suits against customers?

Received summons that states LVNV FUNDINF LCC a debt collector has filed to collect a debit and that i have 28 days to respond Morgan & Pottinger, P.S.C. Is it not correct that a derit collection agency can not sue for debit that is not owed to them? If Capital One is the true holder of this debit then why don't they sue? Lastly when these happen to show up in court it seems they don't show any proof of signuture or ssn# on any documents, isn't that proof to show if you are the true accussed? If then why would any Judge make ruling in there favor? This seems that someone is getting paid under tables because when i had to go up to records there seemed to be a lot of records of Capital One on the counter. - Is this your question? Add additional information