RCS payment allocation issues

Been going well for months and now again I am being told I will be handed over for not paying my account. Yet proof of payment is sent and I pay early as well. A letter and calls again to tell me I am behind on payments. When does this stop? When is the work going to be done properly before accusing someone of not paying their account but then also being dont worry just ignore our harassing calls and emails if you paid already. How does it take you 2 weeks to allocate a payment and then just choose to believe the client is wrong before rectifying?