Missed on credit card minimum payment, now getting calls from debt collector.?

I have a small balance on my credit card and each month pay off either the minimum or slightly more. Last month I was ill at the time the payment was due and forgot until I got the bill for the next month a few days after (payment was due last wed, I recieved the next bill on Mon). This told me I had failed to make the minimum payment and had incured a �12 charge, as I expected. I put it to one side intending to pay as normal next month. Since yesterday (tues) though I have been getting phone calls from a number that it turns out is a debt collection agency. I'm really worried as I've never been in arrears before, despite being a barclaycard customer for over 5 years. Would they hand me over to debt collectors for just missing one payment (my minimum is just over �5 with a balence of just over �200, so we're hardly talking anything bit)? I suffer bad depression so this is just making things worse.