ANSWER:

If you were able to perform wudhu and you did not and instead performed tayammum without a legitimate reason, such prayers are invalid.

You should move on, ask Allah for forgiveness, repent to Allah and feel deep sincere remorse and pledge not to do that again.

QUESTION: In the past I made mistake. When I get sick of typhus and cold, I use tayammum instead of warming up the very cold water that I can’t bear to pray Fajr . How do I fix this now? I’ve been doing that for days in that time, but I don’t know exactly how many times