Some advice please,

[DK387]

I purchased 2 weeks ago via a popular internet auction site a tuning part for my classic car, (its a safety roll-over bar as its a rally car i am building) it was purchased new (old Stock) from a leading manufacturer who was clearing out their warehouse for the new year.
It was advertised for my car model and only to fit my car model and the measurements they provided on my request showed it would fit the exact model i have. The part has been out of mainstream production for some years but they can still produce them with thier CAD CAM machines, the part arrived but was blatently incorrect, i rang to enquire as to whether the wrong part had been sent to me by mistake, and was told not; i checked the fitting in the car (as they requested) and as i suspected it was over 300mm short, i rang to tell them of the problem and they immediately offered to take the part back for a full refund, or they can manufacture a replacement part correctly for a cost of £125 plus the vat.. i paid £45 for the incorrect part they sold to me initially, do i have any other rights other than to accept the refund and reorder a replacement at £125?