What is the ruling on following disbelievers on social media, and chatting with them in writing while they send symbols and words of disbelief, and keeping the conversation? And does sin befall the one to whom words of disbelief reach?

One must be wary of corresponding with those who send objectionable symbols, and refrain from doing so unless there is an overriding benefit, such as gaining worldly knowledge. If blasphemous symbols are sent, they must be deleted immediately. Conversation and correspondence between foreign (non-mahram) men and women, especially disbelievers, is a gateway to tribulation (fitna) and corruption. The general rule is to prohibit it unless there is a need and security from tribulation.