1. Delete snapshot on VMs.
2. Convert VM's VMDK Disk's Type from Thick to Thin via SvMotion.
3. Check if any VM folder showing inside data-store which is already got removed from vCenter/Host Inventory, if yes then delete those folder (do carefully).
Try these steps, It will help you to make free space on your data store 
Regards,
SARIK (Infrastructure Architect)
vExpert 2018-2020 | vExpert - Pro | NSX | Security
vCAP-DCD 6.5 | vCP-DCV 5.0 | 5.5 | 6.0 | vCA-DCV 5 | vCA-Cloud 5 | RHCSA & RHCE 6 | A+ (HW & NW)
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