As an owner, can I list my property

No, if you have appointed a Sole Agency, only the appointed Estate Agent (EA) and its Real Estate Salespersons (RES) can conduct the sale. If you sell the property yourself, the EA is not entitled to commissions. However, if another Estate Agent transacts it, you still have to pay the appointed EA.

For more details, you can visit the CEA Council for Estate Agencies.