I am selling my property, do I still have to pay Service Charges and Ground Rent?

Yes. Whoever is the owner of the property on the date the invoice is due for payment is responsible for paying that invoice in full. This applies even if you are likely to sell your property part way through the period covered by the invoice.
Your solicitor handling your property sale should arrange to collect an appropriate apportionment from the purchaser at completion of your sale.
Please note – any arrears are likely to delay your sale until the arrears have been paid in full.