Generally, a build up of ice in a freezer is caused by the ingress of air (and moisture in the air). The door seals are usually to blame.
Check that you door is straight and attached correctly.
Check the rubber seals for wear. You can normally replace the seals for not a lot of money.
Check that and I will be hear if you need more help.
Thank you for your accept. Please be assured that the experts here do not send emails to past paying customers.
I'll be happy to help you next time.