They claim the price quoted is the BT Wholesale cost price to them. Seems steep to me is all, I thought it was £130...
You must remember that BT Wholesale are not Openreach.
Using the figures you have quoted, Openreach may well have the figure of £130 on their price-list. There is nothing wrong or illegal for BT Wholesale to quote a higher price to your ISP/CP. Nor is their anything wrong or illegal for your ISP/CP to quote a higher price to you . . . as they all want their "cut".
Would you be willing to disclose the new provider, to whom you have migrated, please? Also, what is the product to which you have subscribed?
. . . (current rate = 52 mbps, max rate = 63 mbps) . . .
You must remember that the maximum rate reported, by any CPE device, is just an estimate. The current rate is a true measurement. Depending upon the product to which you have subscribed, there may not be anything more that the circuit "can give". Is it worth the potential expense?