I'm trying to create on Azure Cosmos DB with MongoDB driver, a new collection. I've reached the limit of 100 collection for account cause it's a serverless account. Now I've deleted some old databases and collection a couple of days ago to free up some space, but I continue to receive the same error. What I'm supposed to do to solve the issue?
Serverless accounts are limited to 100 collections per account, documented here in service quotas, https://learn.microsoft.com/azure/cosmos-db/concepts-limits#serverless-1.
If you are expecting more than 100 collections across all databases in the account, I'd recommend using the MongoDB vCore service. Unlike the RU-based model this is single-instance, VM-based, and can be a better fit when migrating existing MongoDB workloads, particularly those with large numbers of small collections. You can start here to learn more, https://learn.microsoft.com/azure/cosmos-db/mongodb/vcore/introduction.