The number of personal credit and charge card accounts open in Australia has fallen sharply from 14.5 million in August to 13.9 million in September - a 4.1 per cent fall.According the latest Reserve Bank payment data, the number of personal credit and charge card accounts is at its lowest level since 2011 and has fallen 6.4 per cent over the past 12 months.The credit card market, along with the whole of the personal finance market, has been in decline for the past few years, with households making it a priority to reduce consumer debt.Increasing use of buy now pay later products appears to be hastening that decline.According to a Roy Morgan Research poll, use of buy now pay later services has grown rapidly over the past year, even though the number of users is still low.Just under two million Australians used a buy now pay later service in the year to September - up from 1.38 million in the previous 12 months. A little under one in 10 people (9.4 per cent) of the population are using buy now pay later payments - up from 6.8 per cent a year ago.The RBA figures show that the number and value of purchases on credit and charge cards has remained fairly steady, despite the fall in the number of accounts. There were 232.7 million credit and charge card purchases in September, worth $21.9 billion.However, balances accruing interest have also been falling steadily. In September, the value of personal credit and charge card accounts accruing interest was $27.7 billion - a reduction of 7.2 per cent over 12 months.