First, check the name of the contributor on the pledge screen. If there is an * next to the contributor's name, please see What do I do if there is an * next to a contributor's name in the Pledge List? for more information.
If the name does not have the "*" then there are some other things you can check. Check the pledge start and end dates. Contributions posted outside of these dates will not be added to the amount given towards the pledge regardless of the fund it is posted to.
You may need to check that all contributions for the contributor were posted correctly. You can look at a list of contributions for a specific person by using the Contributor or Detail Reports.