Agreed. The only way it could affect your credit is I think if the club pursued you in the courts for breaching the contract (basically chasing you for the unpaid amount of the ST) and obtained judgement against you resulting in a CCJ being registered. Highly unlikely they'd do that...
Here's what we have signed up to if on DD scheme. It's pretty clear.
Direct Debit Terms & Conditions
1. The issue and use of a Smartcard Season Ticket is conditional upon the Ticket Holder’s payment of the Season Ticket Fee in cleared funds in advance or subject to the provisions of paragraph...
This. 'I'll happily sign a contract that is advantageous to me (interest free 'loan' for ST purchase rather than payment in full up front) until it doesn't suit me, then through no fault of the club my circumstances will change, and I'll make a huge fuss and say they are *******s for suggesting...
Moaning on here is a bit like complaining about your hotel on tripadvisor when you get home without having done anything about it whilst you're there. Give the club a chance to deal with it, if they don't, then have a pop..........?