First of all well done on securing the job!
I presume that you will be working more than 29 hours a week – if so you will not be entitled to claim Mortgage Interest Supplement, & I wouldn’t expect any leeway in that regard, as it is one of the basic eligibility rules.
You should speak to your CWO & explain the situation to him/her. They really have no interest in credit card repayments – the only bills they get involved with are ESB or Bord Gais.
Considering the circumstances you might qualify for an Exceptional Needs Payment, & if your CWO does not suggest this you should ask them for an application form, & hopefully they can help you that way.
Do you know that you can apply for a Clothing Allowance of €150 for yourself under the SWA scheme? If you haven't already done so you should apply for that now.