You described the problem - the hold for the total amount, the purchases for smaller amounts. Normally, a hold is replaced by a charge for the same amount using the same reference number for the hold, which releases it. In this case, the hold (auth) wasn't re-used, so it's up to your bank's policy on when they release holds. There might be something BA could do, but it would be their payment processor, not them.

You should call your bank and point out that the charge was split into two, it matches, and they should clear their hold. Since it exists in their systems, that shouldn't be a problem.

As others have said, use a credit card next time.