3 bills for transporting a person once!

My dad was transported by hospital via this service and sadly passed on last September 2022. They send me a bill which I agreed to pay. The bill was settled in full and the proof of payment emailed. Since paying I received another bill for the same amount and a diff ref number and also a third bill on my mums phone with a diff ref number. We received sms’s stating that we r going to b handed over for not settling this account. I have send the proof of payment again and also tried reaching out to er24. I’ve received no feedback apology or response or even clarity regarding 3 bills for transporting someone just once. It’s horrible for a family that’s grieving a loss to go thrw this.