Misled on price. STAY AWAY

I brought a set of shocks for my boys mini, had to pay via bank transfer which cost me £15 as the card payment on the site was not working.
I ordered my parts from the main web site, went to checkout and paid the full amount included postage what was requested on the invoice.
An email was then sent to me with an invoice showing my parts and the full cost. Also showing my payment,

After 4 days I emailed them asking if they have received my payment, answer was no!
I email again the next day this time with the info from my bank.
They said yes payment has been received but I am over 40euros short on the payment.
I aske why as I paid the full amoun which was shown on the invoice. They said It might be that I have missed the postage cost (MIGHT). This later changed to "I have not paid the correct amount for the item"
I requested they send me my item as I brought and paid for as sold on the website.
They refused and said they will not pay for my mistakes. I needed to pay the extra via bank transfer to get what I wanted. (This would cost me an extra £15 as they would not allow payment by card)
I request a full refund and wanted my money back.
2 days later they are still sending me emails asking for extra payment even though I requested a refund.
3 days after requesting a refund they agreed to pay me my money back which would take 2 weeks to reach my account.
I am very unimpressed with how I was treated and how they accused me of making mistakes when it was clearly the fault of the company. I have invoices to prove everything from my side.
I'm still waiting for my refund,,,,
NOT HAPPY