Unpaid - what now?

2

I need some advice please regarding some work I haven't been paid for. I am a freelance artist and have recently run some workshops at a local gallery. I was told (via a signed contract) that I would be paid "a month in hand" ie for a workshop mid-June I should expect to be paid (into my bank account) at the end of July. The first workshop was well attended and I got some good feedback - I also enjoyed it very much - so I booked and taught three more workshops soon afterwards. Unfortunately, however, I did not receive any payment at the end of July for the initial workshop. I have asked about this and been told that the bank are at fault but I can't help feeling uneasy, especially since I discovered some online reviewers complaining about this problem. How should I handle this? I would be grateful for your thoughts.