Hopefully, this will end the stalking before it evolves.
First, you must say NO. Even if it is not easy, say NO and stand your ground.
Avoid entering into a dialogue with the stalker.
Everything else than a clear ‘no’ will be construed as an opening by the stalker. This will lead the stalker to believe that he/she just need to put an extra effort into his/her attempts of contacting you until you say ‘yes’.
The stalker will do anything to get in contact with you. Perhaps even threaten suicide. You need to be strong and keep ignoring him/her.
Do not try to convince your stalker that it is for the best if he/she leaves you alone. By negotiating with a stalker who makes you feel uncomfortable or gives you a guilty conscience, his/her expectations and hope for more contact ignite.