Worst customer service

I have been using Payflex for a year now without any issues, but recently i placed an order on the 25th March totalling 1651.00, I paid the 1st instalment of 590.34. Then second instalment was increased to 619.12. I then checked my payflex profile only to realise that they updated my initial instalment as 412.75, second 619.12 and third 619.13……this adjusted instalment means i will end up paying a total of 1828.59 for a total order 1651. I have sent an email to support but they don't come back to me despise their automated email stating that they will provide feedback within 72hrs. I have also tried making phone calls but thats a dead end. I’m disappointed at their customer service or let me rather say the lack of.