Just trying to help out here - I don't have such experience but I'm a qualified accountant so hopefully what I think won't be too far off.
The c285 form you've mentioned seems to be for businesses who import and pay import VAT (the form requires a VAT reg number, which I presume an individual won't have). There is an alternative form called c285CDS if you've used the customs declaration service to import (which is what I think is applicable for you).
The VAT rules states that UK residents need to pay VAT on overseas shopping above £3xx but I don't think it specifies whether a refund can be obtained if the goods are subsequently returned.
What I think you'll find helpful (and it did help me) is to call HMRC and explain the situation. I've had a relatively complex VAT refund issue that I was able to get to the bottom of by calling them.