Vodafone — Harassment for Bill Payment

Vodafone has been harrassing me for a bill paymnet of Rs 542.35. I paid this exact amount on May 10 and I have evidence. Yet they claim this amount is from 3 -4 years ago however they have no evidence of what time period this bill is for. I have paid all my bills on time as can be seen from my history and yet they have been harrassing me with calls and messages to pay this amount but have no bill to show me or any evidence of what this money is for. This is absolutely ridiculous and I want them to immediately stop this.