How Can I Resolve a Duplicate CSCS Account Number on Zedcrest Wealth in Nigeria?

Yes. This can be resolved, and you should not simply continue using the new CSCS account without first asking Zedcrest to correct the duplicate.
The important distinction is:
CHN (Clearing House Number) identifies you as an investor in the Nigerian capital market.
A CSCS account number is associated with your account with a particular stockbroker.
If you already had a CHN/account from InvestNaija and Zedcrest was supposed to link that existing record, but instead created another CSCS account, CSCS has a formal process for merging accounts / CHN consolidation. CSCS currently lists this service at ₦3,000 + 7.5% VAT. �
CSCS +1
What I recommend you do
1. Do not close your old InvestNaija account yet.
First establish which account contains your existing shares and which one Zedcrest created.
2. Contact Zedcrest Wealth and specifically request “CSCS account merger/CHN consolidation.”
Tell them:
I already had an existing CHN and CSCS account through InvestNaija. During my onboarding with Zedcrest Wealth, I provided my existing CHN for linking, but a new CSCS account number was created for me instead. I believe this has resulted in a duplicate CSCS account. I want the new account consolidated/merged with my existing CSCS account and my original CHN retained.
CSCS itself says investors can request a global search through their active stockbroker, which can reveal holdings across brokers and registrars. �
CSCS
3. Ask Zedcrest to do a CSCS Global Search for you.
This is particularly important in your situation because you previously held the InvestNaija account. The global search can establish:
your original CHN;
your old CSCS account;
the new Zedcrest CSCS account;
where your shares are currently sitting;
whether there are actually two separate CSCS records.
CSCS also provides a USSD service that can retrieve your CHN and check stock positions. �
CSCS
4. If Zedcrest says the duplicate cannot be corrected from their end, ask them to initiate the “Merging of Accounts / CHN Consolidation” process with CSCS.
This is an established CSCS account service, so a duplicate does not necessarily mean your shares are lost. �