Hello, Ahmed Imam Attia—No, that sentence is not grammatically correct. The progressive ("haven't been seeing") doesn't work. It should be: "I haven't seen you for ages."
The sentence "I haven't been seeing you for ages" is extremely unnatural and has a silly meaning, namely, that it is not the case that I have been seeing you (repeatedly) for ages. It is incompatible with "I miss you so much."
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