Ridiculous premium calculation that should never have been!

I had to put in a small claim last week, which was dealt with fine, but we found that an old address that we asked to be removed from our business profile in July last year was not done. We therefore were insured at three addresses. Today I thought to rectify their mistake and asked them to remove the third address. The two addresses that remained are the same and all our equipment that was stored at the old address was under all risk cover. Today when Outsurance removed the address they recalculated our premium to an additional R600pm from R1280 to R1874! I think this is absolutely ridiculous and I am disgusted by it. I should have not bothered fixing the policy (spending 40 minutes on the phone doing this). I would have been covered and would have been paying my original premium. If Outsurance cannot see the illogical way they have dealt with this I will be moving insurance companies before month end!