Rob Clark, 66, claims he drove away from the supermarket in Grimsby, Lincolnshire before returning for a second time on the afternoon of September 30.
A few days later, he was stunned to receive a parking fine stating he had remained there for six hours.
Rob's stepson, Ryan Dales, said he felt the fine was unfair amid the cost-of-living crisis, and that his stepdad was left upset by the letter.
Parkingeye - which operates the Asda car park - has now cancelled the charge as a "gesture of goodwill", reports Grimsby Live.
Ryan said: "He went to the store in the morning, left again and then went back in the afternoon. A few days later he got this fine through the door saying he'd been there all day.
"He looked at it and said, 'What? I haven't parked anywhere I shouldn't have'.
"Then when he read into it more, he saw it said he'd been parked in the Asda Grimsby car park for five hours and 58 minutes."
Despite sending bank statements to prove he had entered the shop twice that day, Rob was still told he was required to pay the fine.
Ryan continued: "He's got bank statements to prove that he attended the shop twice that day, and the CCTV in that area would be able to prove that he left and returned to the store.
"On the fine letter, there's a threatening message which says the £70 parking fine would be reduced to £40 if it's paid by a certain time.
"A lot of people would say, 'I'll just pay the fine and forget about it', but it's not fair when people are just returning to a store twice.
"I'm sure if Asda knew what was going on then they wouldn't be too happy about it, because it means people who shop at the store can't return more than once to do their shopping."
Rob was so upset by the fine that he considered paying the discounted £40 charge, said Ryan.
He added: "It seems to me as if it's a threat saying, 'If you want it cheaper, pay it now and don't think about it', so I had to advise him otherwise and told him to challenge it because he didn't even park there all day.
"It angers me. The company clearly has cameras on either side as you're arriving into the car park and leaving it, so they shouldn't be doing this to people at all.
"The way the country is at the minute, it's already scary enough - and this is just making things even worse."
Parkingeye said it has reviewed the case and withdrawn the charge.
A spokesperson said: "The car park at Asda Grimsby has a number of prominent and highly-visible signs that give motorists clear guidance on how to use the car park responsibly, of which the vast majority of them do.
“It appears that this particular motorist stayed beyond the allocated three hour free period, which resulted in them receiving a parking charge notice.
“There is no record of the motorist appealing the parking charge with Parkingeye, however, we have reviewed the case and the charge has been cancelled as a gesture of goodwill.
“Parkingeye are proud members of the British Parking Association (BPA) and strictly follows its guides.
"As part of this we operate the BPA audited appeals process, which motorists can use to appeal their parking charge. If anyone has mitigating circumstances then we would encourage them to contact us."