A customer game me a cheque in payment for a service each month for a year, but I didn't cash them when they were given to me.

I'm not sure if I have the cheques anymore and I'm not even sure if they are cancelled now, and when I asked the customer if they can transfer the money to me he said that it's my fault for not cashing the cheques and now he's unable to pay the full amount (just under £500) in one go. I asked if he could make payment in 2 or 4 installments but he said he didn't sign a written contract to pay and now refuses to pay at all.

Am I still entitled to pursue payment? Can I demand that he pays it all in one go? What do I need to do before taking him to a small claims court?

If I'm not entitled to ask the customer for alternative payment, then if I find the cheques but he has cancelled them then does that give me any standing to demand payment even after a year?

Thanks,
Tim