Amsterdam city council has increased the supervision of its local finance office, saying technical failings and human error were to blame for last month’s over payment to nearly 10,000 poor households.

Last month it emerged 10,000 households were wrongly paid thousands of euros in extra housing benefit, costing the city €188m. Some people expecting a €155 payment received €15,500 instead. The highest wrong payment was €34,000.

‘This should never have happened,’ finance alderman Pieter Hilhorst said on Monday. All but €2.4m of the €188m in wrongful payments has now been recovered.

According to research by KPMG, the software used by the city council to regulate the payments – an extra housing benefit for the city’s poorest households – is based on cents rather than euros.

No one had spotted the error, which led the system to generate payments of €188m rather than €1.8m. Experts expect up to €1.2m of this will be very difficult to recover. In addition, the city has spent €300,000 trying to rectify the situation, news agency ANP reports.