You can easily check, just price up the flights on ba.com in W and then in J. Look at the price breakdown on the quote page and you should see if there is a difference and what it is - from W to J it will be carrier surcharge.

Tbh for that route £190 sounds correct. I don’t know how you managed it for your own booking at no extra cash - unless you did it at the time of booking and effectively paid the extra at that point. Has your reticketed?