City Blinds: City Blinds after sales service

Recently I took a blind made by City Blinds to the shop to have a slat replaced, but the lady behind the counter refused and made it very difficult for me to order a new one, so I took it back home and repaired as best I could. Now another blind, from the same bay window, needs to have the cord replaced. What can I do to have the blinds repaired by them? That lady seems to be there all the time and I live in West London so getting there involves crossing London in heavy traffic. I cannot risk finding her there as I know she will not be helpful and will try to refuse taking them in. The blinds were expensive (part of a very large bay window) and I don't want to replace them, especially the large, middle one, as I think they are easily repairable and I don't mind the cost.

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