I took out a Tesco credit card recently (interest free for six months and all that) to cover me while I wait for some money I have coming my way in August. I signed a direct debit mandate form with Tesco to deduct the min balance each month. However, they deduced a full 3000 this month and ran me into an unauthorised overdraft with my bank (TSB). I was furious. They have admitted they were in the wrong as the mandate form was very very clearly marked min balance only. They have agreed to transfer the money back but this is taking forever. In the meantime, I'm still in an unauthorised OD with TSB. Will this affect my credit rating??