Undue enrichment-Charging for services not rendered

I have received a bill from Jackpersad and Partners for a procedure done. I thereafter took the bill with the reference and paid the account however the amount was paid in error to Lancet Laboratories. I have received a call from Jackpersad last year stating that the bill has not been paid, I then proceeded to correct this error by contacting Lancet Laboratories to rectify the this issue. When I did so I was under the impression Lancet Laboratories refunded Jackpersad for the money due to them, however they failed to do so. Lancet has taken the amount paid to them in error and refuses to refund me back the money which was NOT due to them as now they are saying that they cannot find that reference number which the money has been paid into and it has been archived. Further to that I am now being threatened to be registered with the credit bureaus for an amount which I have paid and this is ridiculous.