It does happen. Years ago I knew someone at work who bought a bra from somewhere similar to what the OP describes. It didn’t fit so she returned it - or thought she had. She was going through a divorce at the time and had other problems so hadn’t realised that the parcel hadn’t been taken to the PO as she misremembered, but was tidied away and left in a drawer for ages.
As with the OP, she had a lot going on financially because of the divorce, and didn’t notice the payments coming out of her account. When she did notice she stopped them, thinking that the bra had been returned. Later, she applied for a mortgage in her own name and was horrified to find that she was refused because of what showed as an unpaid debt. The payments she had made for the bra more than covered the cost of it, but the interest mounted after the payments stopped, and late fees were added each month.
I can’t remember what happened in the end, but it was out of all proportion to the cost of a bra - particularly as she could have afforded to pay outright and as it didn’t fit anyway.
Her fault, no doubt- but these things do happen, particularly when people are under stress.